SOIL GUIDELINE VALUES FOR NAPHTHALENE CONTAMINATION

Transcription

1 Department for Environment, Food and Rural Affairs The Environment Agency SOIL GUIDELINE VALUES FOR NAPHTHALENE CONTAMINATION

2 Publishing Organisation Environment Agency, Rio House, Waterside Drive, Aztec West, Almondsbury, BRISTOL, BS32 4UD. Tel: Fax: Website: Environment Agency 2005 November 2005 ISBN All rights reserved. No part of this document may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of the Environment Agency. Officers, servants or agents of the Environment Agency and Department of Environment, Food and Rural Affairs, accept no liability whatsoever for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained herein. Dissemination Status Internal: Released to Regions External: Released to Public Domain Statement of Use This publication sets out the derivation of the Soil Guideline Values for naphthalene contamination. The report has been written for technical professionals who are familiar with the assessment and management of the risks posed by land contamination to human health. It is expected to be of use to all parties involved with or interested in contamination, but in particular to those concerned with the assessment of land contamination. Keywords Soil Guideline Values, naphthalene, polycyclic aromatic hydrocarbons, PAH, land contamination, priority contaminants, risk assessment. Research Contractor This document was produced by: URS Corporation Ltd Alpha Tower, 7th Floor, Suffolk Street, Queensway, Birmingham, B1 1YQ Tel: Fax: Environment Agency Contact Ian Martin, Principal Human Health Scientist, Ecosystems & Human Health Science Group, Environment Agency, Olton Court, 10 Warwick Road, Olton, Solihull, B92 7HX Further copies of this report can be obtained from the Environment Agency's National Customer Contact Centre by ing enquiries@environment-agency.gov.uk or by telephoning

3 Contents 1 Introduction Naphthalene in the environment... 6 Chemistry of naphthalene... 6 Sources of naphthalene... 6 Behaviour in the soil environment... 8 Potential for harm to human health and relevant health criteria values for soil Soil Guideline Values for naphthalene Purpose Land use Soil Guideline Values according to land use Further information for assessors who apply these Soil Guideline Values Mobility of naphthalene in the environment Other considerations including acute exposure Comparison with other approaches References List of tables Table 1.1 Assessment of risk to human health from land contamination. Key reports from Defra and the Environment Agency Table 2.1 Physical-chemical properties of naphthalene (Environment Agency 2004a, IUPIC-NIST 2003)... 9 Table 2.2: Tolerable Daily Intakes (TDI) and Adult Mean Daily Intakes (MDI) derived from oral and inhalation studies Table 3.1 A brief description of the standard land-uses for Soil Guideline Values.. 16 Table 3.2 Soil Guideline Values for naphthalene as a function of land-use Table 3.3 Contribution to total exposure from soil for the relevant pathways expressed as a percentage of the mean exposure calculated by the CLEA model... 19

4 1 Introduction 1.1 This report is one of a series of documents issued by the Department for Environment, Food and Rural Affairs (Defra) and the Environment Agency. The main purpose of the Contaminated Land Reports (CLR) series is to provide regulators, developers, landowners and other interested parties with relevant, appropriate, authoritative and scientifically based information and advice on the assessment of risks that arise from the presence of soil contamination. 1.2 This report describes soil guideline values (SGVs), generic assessment criteria for assessing the risks to human health from chronic exposure to soil contaminated with naphthalene. It is essential that the information presented here be used in conjunction with an understanding of the main reports in this series (see Table 1.1) and in the wider context of assessing environmental risk (DETR, Environment Agency and IEH, 2000). 1.3 This technical material can be used in support of the application of the statutory regimes that address land contamination, especially Part IIA of the Environmental Protection Act (EPA) 1990 (the contaminated land regime) and development control under the Town and Country Planning Acts (DETR, 2000; ODPM, 2004). See paragraphs 3.1 to 3.3 for further information. 4

5 Table 1.1 Assessment of risk to human health from land contamination. Key reports from Defra and the Environment Agency. CLR7 Assessment of Risks to Human Health from Land Contamination: An Overview of the Development of Soil Guideline Values and Related Research (Defra and Environment Agency, 2002a). CLR7 serves as an introduction to the other reports in this series. It sets out the legal framework, in particular the statutory definition of contaminated land under Part IIA of the Environmental Protection Act (EPA) 1990, the development and use of SGVs and references to related research. CLR8 Priority Contaminants for the Assessment of Land (Defra and Environment Agency, 2002b). This identifies priority contaminants (or families of contaminants), selected on the basis that they are likely to be present on many current or former sites affected by industrial or waste management activity in the UK in sufficient concentrations to cause harm, and that they pose a risk, to any of human health, buildings, water resources or ecosystems. It also indicates which contaminants are likely to be associated with particular industries. CLR9 Contaminants in Soil: Collation of Toxicological Data and Intake Values for Humans (Defra and Environment Agency, 2002c). This report sets out the approach to the selection of tolerable daily intakes (TDIs) and Index Doses for contaminants to support the derivation of SGVs. CLR10 The Contaminated Land Exposure Assessment Model (CLEA): Technical Basis and Algorithms (Defra and Environment Agency, 2002d). This report describes the conceptual exposure models for each standard land use that are used to derive the SGVs. It sets out the technical basis for modelling exposure and provides a comprehensive reference to all default parameters and algorithms used. TOX 20 Contaminants in Soil: Collation of Toxicological Data and Intake Values for Humans. Naphthalene (Defra and Environment Agency, 2003). This report details the derivation of the oral and inhalation based tolerable daily soil intakes (TDSI) for naphthalene. Environment Agency (2004a) Update on the dermal exposure pathway, Briefing Note 1. Environment Agency (2004b) Update on estimating vapour intrusion into buildings, Briefing Note 2. Environment Agency (2004c) Update of supporting values and assumptions describing UK building stock, Briefing Note 3. Environment Agency (2005) An update on deriving soil guideline values based on combined intake from individual routes of exposure, Briefing Note 4. This document: SGV 19 Soil Guideline Values for Naphthalene Contamination. This report presents the SGVs for naphthalene and sets out their derivation. 5

6 2 Naphthalene in the environment Chemistry of naphthalene 2.1 Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds that consist of two or more fused benzene ring structures in various arrangements (Environment Agency, 2003). Naphthalene (C 10 H 8 ) is the simplest PAH in the group, and consists of two benzene rings (see Figure 1.1). At room temperature, naphthalene is a white crystalline solid with a strong tar-like odour (ATSDR, 1995; Defra and Environment Agency, 2003). It has a low volatility and water solubility. It has also been known as tar camphor, albocarbon, naphthene, mothballs, mothflakes and white tar (ATSDR, 1995; Environment Agency, 2003). Figure 1.1 Chemical structure for naphthalene (Environment Agency, 2003). Sources of naphthalene 2.2 Naphthalene is prepared from coal tar by crystallisation and distillation with an estimated 12,000 tonnes per annum being produced in the UK during 1990 (EU, 2003). Distillation of coal tar produces several fractions, including naphthalene oil, which is the most abundant source of naphthalene (up to 50 per cent by weight). Naphthalene oil is processed by further distillation and by treatment with sulphuric acid to make a purer grade product (EU, 2003). 2.3 The total volume of naphthalene that enters the UK market from production and imports has been estimated to be tonnes per annum (EU, 2003). It is used as an intermediate chemical in the production of phthalic anhydride (used to make plasticizers, resins, dyes, pharmaceuticals and insect repellents) and in the production of insecticides, synthetic leather tanning agents, dyes, resins and surface active agents (ATSDR, 1995; 6

7 EU, 2003). Naphthalene has historically been the active agent in mothballs as an insect repellent (EU, 2003). 2.4 Like other members of the PAH family, naphthalene is also formed as the result of pyrolytic processes, especially the incomplete combustion of organic materials, which is the greatest source of emissions of naphthalene into the environment (WHO, 1998; Defra and Environment Agency, 2003). Although natural sources such as forest fires and volcanoes do emit PAHs, the largest contribution is from anthropogenic activities, such as the burning of fossil fuels for heating, light and transport 1, the processing of coal, crude oil and gas as a chemical feedstock, treatment of wood with preservatives and waste combustion (Environment Agency, 2003). The historical processing of coal for the production of carbon blacks, creosote, coal tar and bitumen is strongly associated with the emission of naphthalene and three-ring PAHs, such as phenanthrene (Environment Agency, 2003). 2.5 Although atmospheric transport and subsequent deposition of naphthalene has resulted in widespread environmental contamination, levels of it and other PAHs in soil are typically higher in urban areas (as a consequence of higher traffic and population densities) or close to current and historical industrial sources than in rural locations (Environment Agency, 2003). Environment Agency (2002b) reported soil concentrations of naphthalene as part of the Countryside Survey 2000 in the range mg kg 1, with a mean of 0.03 mg kg 1. This is consistent with a range of studies for England and Wales cited by EU (2003). 2.6 While surveys of rural and urban soils demonstrate the ubiquitous presence of naphthalene in the environment (WHO, 1998), the difference in levels of contamination between diffuse pollution and point sources should not be under estimated. Environment Agency (2003) reported naphthalene soil concentrations in the range mg kg 1 for a number of industrial sites in Europe and the USA. 1 EU (2003) estimated that diesel-powered lorries emit as much as 9.2 mg naphthalene per kilometre travelled. 7

8 Behaviour in the soil environment 2.7 A comprehensive review of the fate and transport of selected contaminants in the soil environment, including naphthalene, has been published by the Environment Agency (2003) and only a summary is provided here. 2.8 Naphthalene is the lightest PAH and is considered by most authoritative organisations to be one of the most mobile relative to other family members. Its transport in soil is moderately retarded by sorption to organic matter (Environment Agency, 2003). However, there is considerable variation between measured and theoretical values for the organic carbon water partition coefficients (K oc ) reported in the literature (in the range cm 3 g 1 ). Its low aqueous solubility and strong tendency to partition to the vapour phase suggests that naphthalene is likely to volatilise from water bodies and surface soils to ambient air (WHO, 1998; EU, 2003). Naphthalene is susceptible to photochemical oxidation by hydroxyl radicals, nitrogen oxides and ozone in the atmosphere, with reported half-life values of less than one day (ATSDR, 1995; EU, 2003). 2.9 The physical and chemical properties of naphthalene used to derive the SGVs in this report are listed in Table 2.1. The observed or predicted values for many of these parameters vary in the scientific literature and those in Table 2.1 were selected to be appropriate for the derivation of SGVs (Environment Agency, 2003) Environment Agency (2003) reported that two- or three-ring PAHs, such as naphthalene and fluorene, have been shown to be degraded extensively in soil under aerobic conditions. The reported range of half-life values 2 of naphthalene in soil and groundwater is wide, from as little as a few days to 765 days under aerobic and anaerobic conditions (USEPA, 1999; Mackay et al., 2000; Environment Agency, 2002a, 2003) The US Environmental Protection Agency (USEPA, 1999) reviewed aerobic biodegradation half-life values for naphthalene in a number of laboratory and field studies with the majority of observations in the range days. USEPA (1999) concluded that naphthalene was rapidly degraded by indigenous micro-organisms in soil and 2 Degradation rates for many organic compounds can be approximated as first-order rate constants (Environment Agency, 2003), where it is assumed that the rate of degradation is proportional only to the contaminant concentration. It is recognised that in reality the situation is much more complex. 8

9 groundwater that had previously been acclimated to PAHs. Note that USEPA (1999) included a considerable number of laboratory-based studies in which degradation conditions may well have been optimised. Table 2.1 Physical and chemical properties of naphthalene (Environment Agency, 2003; IUPAC-NIST, 2003). Parameter Units Value Molecular weight g mol Boiling point K 491 Aqueous solubility a mg l 1 19 Vapour pressure b Pa 37 Henry s Law constant b atm m 3 mol x 10 4 Octanol water partition coefficient (log K ow ) unitless 3.37 Organic carbon water partition coefficient (log K oc ) unitless 3.11 Coefficient of diffusion in air b m 2 s x 10 6 Coefficient of diffusion in water b m 2 s x Enthalpy of vaporisation cal mol Critical temperature K Dermal absorbed fraction unitless 0.13 a Value reported at 283K based on Solubility Database (IUPAC-NIST, 2003). b Value reported at 298K. Adjusting for Soil Temperature in the Soil Vapour Model The soil vapour algorithms used in the Contaminated Land Exposure Assessment (CLEA) model should, where possible, be adjusted to take into account the soil temperature. The default value used in the CLEA model is 10 C (Environment Agency, 2004b). The three chemical properties that are adjusted are Henry s Law constant, maximum aqueous solubility and saturated vapour pressure. Environment Agency (2003) reports the most authoritative values for each of these parameters, which are normally measured at temperatures of 20 or 25 C. While Henry s Law constant can be adjusted automatically within the CLEA model to account for the lower soil temperature, the other parameters must be estimated outside of the model. At 25 C, the authoritative value of the vapour pressure of naphthalene is 37 Pa (Environment Agency, 2003). Calculated methods to adjust vapour pressure according to temperature, such as the Antoine Equation method (Boethling and Mackay, 2000) have an applicable range in the order of 1000 to Pa. It is therefore not appropriate to adjust the vapour pressure for naphthalene from the authoritative value previously identified Environment Agency (2002a) reviewed field study data and concluded that half-life values for aerobic degradation of naphthalene were in the range days for shallow sand and gravel aquifers within the concentration window of 10 µg l 1 to 30 mg l 1. However, Environment Agency (2002a) also noted that significant slowing of degradation was likely 9

10 at low concentrations due to bioavailability constraints and that under anaerobic conditions there was frequently no degradation. Environment Agency (2003) cautioned against the use of first-order rate constants to describe the degradation of PAHs because of the biphasic nature of their sorption to soil organic matter and the effect that bioavailability has on biodegradation processes Biodegradation processes for naphthalene in soil have therefore not been taken into account in the derivation of the SGVs in this report In modelling dermal exposure, the CLEA model recently adopted the approach advocated by the USEPA of using dermal absorption fractions (DAFs) derived from experimental studies that involved soil (Environment Agency, 2004a). The high lipophilicity of PAHs means that they are able to penetrate skin, and dermal absorption from soil can be a significant exposure pathway (Environment Agency, 2003). USEPA recommended an experimentally based DAF of 0.13 for benzo[a]pyrene and other PAHs, which was used in the derivation of SGVs in this report (Environment Agency, 2003) In the urban background atmosphere, between 70 and 90 per cent of PAHs by weight are associated with dust particles less than 3 µm in diameter (Environment Agency, 2003). However, in the case of naphthalene, its volatility and moderate preference to sorb to soil organic matter means that the inhalation of dust is not likely to be an important pathway for human exposure relative to the inhalation of vapour from soil 3. Vapour intrusion into buildings has been modelled using the Johnson and Ettinger (1991) algorithms and default assumptions as described in Environment Agency (2004b, 2004c). 3 EU (2003) observed that the relative importance of gaseous and particulate air concentrations of naphthalene depends to an extent on the original source characteristics. 10

11 2.16 Taken as a chemical group, plant uptake of PAHs is likely to be driven by atmospheric deposition of contaminated dusts and through plant contact with, and entrainment of, soil in near-surface and below-ground plant parts (Environment Agency, 2003). However, as noted earlier naphthalene is more mobile than many other PAHs and its uptake into plants may involve a greater contribution directly from passive root uptake or indirectly after volatilisation of the chemical from the soil and subsequent vapour phase sorption onto plant surfaces. There are very limited data on the uptake of naphthalene by plants and few specific studies were found that relate to the garden vegetables considered in the CLEA model (Environment Agency, 2003). Studies by Wild and Jones (1991), Fismes et al. (2002) and Kipopoulou et al. (1999) detected the presence of naphthalene in cabbages, carrots, lettuces and leeks grown in contaminated soils. Bernillion et al. (2002) studied the uptake of PAHs by garden vegetables from soils contaminated with coal tar, commenting that it was difficult to study naphthalene and other light molecular weight PAHs because of their relative mobility compared to heavier members of the group Based on its chemical properties, naphthalene lies within the calibration range of screening models for assessing plant uptake, such as those of Briggs et al. (1982, 1983), Ryan et al. (1988) and Trapp and Matthies (1995). Samsøe-Petersen et al. (2003) evaluated use of such models to estimate the plant uptake of naphthalene from soil and concluded that they tended to over-predict plant uptake of PAHs by about a factor of Using a dynamic uptake model specific to potato, Samsøe-Petersen et al. (2003) estimated soil-to-plant concentration factors for naphthalene of the order of 0.14 µg kg 1 plant per µg kg 1 soil on a fresh-weight basis. The more general Briggs et al. (1982, 1983) approach currently used in the CLEA model (Environment Agency, 2002d) estimates soilto-plant concentration ratios for potato between 0.34 and 1.6 µg kg 1 plant per µg kg 1 soil over the range 1-5 per cent organic matter content (and measured at the concentration of the respective SGVs in Table 3.2 for the allotment land-use scenario) 4. This suggests that predicted uptake from the soil solution is broadly consistent between the models and also with the theoretical considerations noted in the literature (Environment Agency, 4 Combined with the partitioning of the chemical between soil, soil solution and vapour phases (Environment Agency, 2004b), the Briggs et al. (1982, 1983) approach takes into account the presence of organic matter, with a higher organic carbon content resulting in lower plant uptake of naphthalene. 11

12 2003). The Briggs et al. approach has been used to derive the SGVs in this report. See paragraphs for a further discussion of uncertainty in modelling this pathway It is unusual for naphthalene to occur in isolation in a contaminated soil because the historic activities with which it is associated usually involve a number of chemicals. In contrast, fate and transport calculations, such as those used by the CLEA model, normally assume single-component behaviour. Naphthalene is found in soil from a variety of contamination sources and is associated with other PAH compounds and complex materials, such as coal tars. Its environmental behaviour is influenced by the presence of other compounds in such a mixture (Environment Agency, 2003). Potential for harm to human health and relevant health criteria values for soil 2.20 The principles behind the selection of health criteria values (HCVs) and the definition of concepts and terms used are outlined in R&D Publication CLR9 (Defra and Environment Agency, 2002c). Information on the toxicity of naphthalene and reasons behind the selection of the most appropriate HCVs for the derivation of this set of SGVs are described in Contaminants in Soil: Collation of Toxicological Data and Intake Values for Humans. Naphthalene (Defra and Environment Agency, 2003). Reference to these documents is necessary to understand the information presented below The literature on the toxicity of naphthalene has been reviewed by the European Commission, the International Programme on Chemical Safety (IPCS), the International Agency for Research on Cancer (IARC), the US Agency for Toxic Substances and Disease Registry (ATSDR) and USEPA. Lipophilic PAHs can be absorbed by the body through the lungs, the gastrointestinal tract and the skin and the limited human and laboratory animal data for naphthalene appear to support this more general statement (Defra and Environment Agency, 2003). After absorption, there is limited and somewhat inconsistent data on the distribution of naphthalene throughout the body. Its metabolism is reportedly complex with most metabolites excreted in faeces or urine (Defra and Environment Agency, 2003) Deliberate ingestion of mothballs containing naphthalene has resulted in symptoms of acute toxicity including nausea, vomiting, lethargy, ataxia, convulsions, abdominal pain 12

13 and evidence of haemolytic anaemia, and liver and kidney toxicity (ATSDR, 1995; WHO, 1998; EU, 2003). In extreme cases, ingestion of mothballs has resulted in coma and death, with the acute lethal dose in adults reportedly in the range mg kg 1 body weight (Defra and Environment Agency, 2003). Infants have also died as a result of haemolytic anaemia after inhalation and dermal exposure to naphthalene in treated clothing, nappies and blankets (ATSDR, 1995; WHO, 1998) The chronic toxicity of naphthalene has been reported in several studies in which residents had been exposed as a result of using a large number of mothballs about the home (Defra and Environment Agency, 2003). Reported health effects included anaemia and kidney toxicity. The key animal studies reported reductions in animal body weight, possible liver, kidney and thymus damage, transient maternal neurotoxicity and minor effects on the blood where naphthalene was administered orally. In inhalation studies the critical effects included increased incidences of benign lung and nasal tumours and neuroblastomas ( nerve tumours ) of the nasal system (Defra and Environment Agency, 2003) IARC (2002) classified naphthalene as possibly carcinogenic to humans (Group 2B) on the basis of inadequate evidence in humans and sufficient evidence in experimental animals. In animal studies, exposure to naphthalene via inhalation resulted in a higher incidence of benign lung tumours in mice and of neuroblastoma of the nasal olfactory epithelium and adenoma of the nasal respiratory epithelium in rats (Defra and Environment Agency, 2003). The general authoritative opinion is that naphthalene is not genotoxic and that tumours are likely to have been induced through localised chronic tissue injury (Defra and Environment Agency, 2003) Thus, the critical health effects of naphthalene are considered to have a threshold and the tolerable daily intake (TDI) values in Table 2.2 are derived from both oral and inhalation studies respectively The oral TDI in Table 2.2 is based on the recommendation of USEPA (1998) and ATSDR (1995). USEPA (1998) derived a reference dose based on the results of an animal study in which the no observable adverse effect level (NOAEL) was established for the critical health effects of reduced body weight and possible kidney and thymus damage. ATSDR 13

14 (1995) derived an intermediate minimal risk level (MRL) from the low observable adverse effect level (LOAEL) of changes in liver function observed in a mice study. The critical health effects observed from oral studies are considered to result from systemic uptake (Defra and Environment Agency, 2003) The inhalation TDI in Table 2.2 is based on the recommendation of USEPA (1998) in deriving a reference concentration in air. USEPA (1998) derived this guideline on the basis of a LOAEL from a rat study, in which the critical health effect was proliferative repair in the nasal respiratory epithelium (a precursor to tumour induction). Assuming a 70 kg adult inhales 20 m 3 of air daily, the reference concentration of 3 µg m 3 can be converted into an inhalation-based TDI of 0.86 µg kg 1 body weight day 1. The critical health effects observed from inhalation studies are considered to be specific to that exposure route only, and Defra and Environment Agency (2003) noted that... exposures that do not induce local tissue damage will not pose any cancer risk Based on currently available information, background exposure to naphthalene from nonsoil sources is relatively low. The largest contribution is believed to come from the consumption of fish and fatty foods such as butter and cheese, lard and margarine, and meat and poultry (Defra and Environment Agency, 2003). Vehicle emissions to ambient air are also considered another major source of human exposure. Nevertheless, background intakes of naphthalene from estimated concentrations in food and ambient air is less than two per cent of the oral TDI and nine per cent of the inhalation TDI for children between the ages of nought and six years, and about 0.5 per cent and one per cent for adults. Table 2.2 Tolerable daily intakes (TDI) and adult mean daily intakes (MDI) derived from oral and inhalation studies. Oral TDI Inhalation TDI (µg kg 1 Oral MDI body weight day 1 (µg day 1 (µg kg 1 Inhalation MDI body weight ) ) day 1 (µg day 1 ) )

15 3 Soil Guideline Values for naphthalene Purpose 3.1 SGVs are a tool for use in the assessment of land affected by contamination. They can be used to assess the risks posed to human health from exposure to soil contamination in relation to land use. SGVs are concentrations of a substance in soil at or below which human exposure can be considered to represent a tolerable (where the relevant HCV is a TDI) or minimal (where the HCV is an Index Dose) level of risk (Defra, 2005), if properly applied as part of a comprehensive risk assessment. Exceeding an SGV can indicate to an assessor that further assessment or remedial action may be needed. 3.2 When using SGV in connection with Part IIA of the Environmental Protection Act 1990 (the contaminated land regime), it is essential to do so in line with the statutory guidance, including in particular B.45 to B49 and Table B of that guidance (DETR, 2000). It is also important to note that soil concentrations above an SGV, properly applied, may not equate directly to unacceptable intake in Table B. When used in connection with planning and building control, the guidance connected with those regimes should be consulted (ODPM, 2004). Additional advice on applying Soil Guideline Values in the regulatory context, including Part IIA of EPA 1990, can currently be found in Soil Guideline Values and the Determination of Land as Contaminated Land, CLAN 2/05 (Defra 2005). 3.3 If used correctly, soil concentrations that exceed an SGV can indicate a potentially significant risk to human health. However, this does not necessarily imply that there is an actual risk to health, and the assessor should take into account site-specific circumstances. Furthermore, if incorrectly applied to a site where the critical pathway or chemical form of the contaminant is not one that has been evaluated to date, a potentially significant risk might be present even though a SGV is not exceeded. So it is important that a risk assessor uses SGVs as a component of an overall risk assessment and management strategy for a site in accordance with good practice (DETR, Environment Agency and IEH, 2000; Defra and Environment Agency, 2004) and, in particular, an appropriate sampling and testing strategy (Defra and Environment Agency, 2002a). 15

16 Land use 3.4 SGVs have been developed on the basis of many critical assumptions about possible exposure to soil contamination and the development of conceptual exposure models to describe different land uses. The standard land uses considered are described briefly in Table 3.1. It is important that an assessor understands these conceptual models and is aware of their assumptions and limitations before applying SGVs to an area of land. Please refer to The Contaminated Land Exposure Assessment (CLEA) Model: Technical Basis and Algorithms and Briefing Notes for a detailed description of the CLEA model on which these SGVs are based (Defra and Environment Agency, 2002d; Environment Agency, 2004a, 2004b, 2004c). Table 3.1 A brief description of the standard land uses for Soil Guideline Values. Further information on the conceptual exposure models for each land use can be found in Defra and Environment Agency (2002d), and Environment Agency (2004a, 2004b, 2004c). Residential People live in a wide variety of dwellings, including, for example, detached, semi-detached and terraced properties up to two storeys high. This land use takes into account several different house designs, including buildings based on suspended floors and ground-bearing slabs. It assumes that residents have private gardens and/or access to community open space close to the home. Exposure has been estimated with and without a contribution from eating home-grown vegetables, which represents the key difference in potential exposure to contamination between those living in a house with a garden and those living in a house where no private garden area is available. Allotments Provision of open space, commonly made by the local authority, for local people to grow fruit and vegetables for their own consumption. Typically, each plot is about one-fortieth of a hectare, with several plots to a site. Although some allotment holders may choose to keep animals, including rabbits, hens and ducks, potential exposure to contaminated meat and eggs has not been considered. Commercial and industrial There are many different kinds of workplace and work-related activities. This land use assumes that work takes place in a permanent two-storey building, factory or warehouse in which employees spend most time indoors involved in office-based or relatively light physical work. This land use is not designed to consider those sites that involve 100 per cent hard cover (such as car parks), where the risks to the site-user are from ingestion or skin contact, because of the implausibility of such exposures arising while the constructed surface remains intact. Further guidance on the limitations in applying this land use to different industries can be found in Defra and Environment Agency (2002d). 16

17 Soil Guideline Values according to land use 3.5 The SGVs were estimated using the CLEA model, in which certain parameters, such as body weight, are treated probabilistically. An SGV is the concentration at which predicted exposure equals the relevant HCV for each standard land use. Since the final exposure is itself a distribution of values, a point in this distribution is chosen for comparison with the relevant HCV. 3.6 In deriving the SGVs in this report, the probabilistic parameters in the CLEA model are sampled 1000 times using a Latin hypercube approach (Iman and Conover, 1982; Iman et al., 1982a, 1982b) and the 95th percentile of the predicted exposure compared with the HCV (Defra and Environment Agency, 2002d). 3.7 The SGVs for naphthalene contamination are summarised in Table 3.2. The values reported in Table 3.2 were rounded to the nearest one or two significant figures. For residential and allotment land uses, SGVs are set to protect young children because, in general, children are more likely to have higher exposures to soil contaminants. For commercial and industrial land use, an adult is assumed to be the critical receptor, with exposure considered over the working lifetime. 3.8 SGVs, including those for naphthalene presented in this report, are based on the updated description of a sandy soil described in Environment Agency (2004b). The availability of naphthalene to plants (as modelled by Briggs et al., 1982, 1983) and its partitioning to the vapour phase (as modelled by Johnson and Ettinger, 1991) depend on the organic matter content of the soil. This is because sorption to organic matter retards volatilisation and uptake into plants from soil solution. Therefore, where vapour pathways or plant uptake are significant contributors to total exposure, an increase in soil organic matter results in a considerable increase in the SGV 5. In addition, the partitioning of contaminants and their movement into vegetable plants and buildings depend on other soil properties, including porosity and saturated hydraulic conductivity, and therefore SGVs for the residential and 5 It is important that assessors obtain analyses for this soil property that are representative of the site and consider whether changes in site conditions are likely to result in significant differences. 17

18 commercial and industrial land-use scenarios vary according to other soil types described in Environment Agency (2004b). Table 3.2 Soil Guideline Values for naphthalene as a function of land use. Standard land use Soil Guideline Value (mg kg 1 dry weight soil) 1 per cent 2.5 per cent 5 per cent SOM SOM SOM Residential and allotments Commercial and industrial Notes 1. Based on the total naphthalene concentration in soil and not applicable to other PAHs. 2. Based on sandy soil as defined in R&D Publication CLR10 (Defra and Environment Agency, 2002d) and subsequently revised in Environment Agency (2004b). 3. SGVs for naphthalene will vary according to soil organic matter content (SOM) for all land uses. 4. It is assumed that the inhalation TDSI applies to a local health effect and the SGV in each case is the lower of the individual oral and dermal criterion and inhalation criterion (Environment Agency, 2004d). Further information for assessors who apply these Soil Guideline Values 3.9 In applying the SGVs for naphthalene to a contaminated site, assessors will find the advice presented in the following paragraphs useful. It is good practice for risk assessors to accompany their risk assessment with an appropriate risk evaluation, including a clear statement of whether representative soil concentrations from the site exceed any generic or site-specific assessment criteria (DETR, Environment Agency and IEH, 2000; Defra and Environment Agency, 2004). In using SGVs it is essential that the assessor reviews the wider context, as discussed in paragraphs The assessor is referred to R&D Publication TOX 20 (Defra and Environment Agency, 2003) for a detailed explanation of the derivation of the HCV used in this report, and of the attendant uncertainties. This is important, especially when considering whether exceeding a SGV is significant. 18

19 3.11 The SGVs presented here are based on considerations of oral, dermal and inhalation exposure. The proportion of exposure attributable to each pathway for each standard land use at the soil concentration of the SGV is summarised in Table 3.3. Table 3.3 Contribution to total exposure from soil for the relevant pathways expressed as a percentage of the mean exposure calculated by the CLEA model. Exposure pathway Contribution to exposure from soil according to land use ( per cent) Residential Residential with Commercial and without plant Allotments plant uptake industrial uptake Ingestion of soil and indoor dust Consumption of home-grown vegetables and ingestion of soil attached to vegetables Indoor and outdoor dermal contact Indoor and outdoor inhalation of dust Indoor and outdoor inhalation of vapour < <0.1 <0.1 <0.1 < < Notes 1. Based on sandy soil with a soil organic matter content of 2.5 per cent (contributions vary slightly with changes to organic matter content). 2. indicates that this pathway is not included in the conceptual model for the standard land use The dominant exposure pathways that drive the risk in this set of SGVs are consumption of home-grown produce and vapour intrusion into buildings. The consumption of homegrown vegetables contributes between 92 and 99 per cent of total exposure in the standard residential and allotment land uses, respectively. As noted in paragraph 2.16, there is a paucity of information on the uptake of naphthalene and other industrial organic contaminants by plants, including garden produce Although a number of screening models are available to estimate plant uptake of nonionised organic chemicals from soil (Environment Agency, in preparation), there are also large uncertainties in predicting uptake of individual chemicals by specific plants, including fruit and vegetables To predict uptake of naphthalene, the CLEA model uses the screening approach proposed by Briggs et al. (1982, 1983), which related the concentration in the plant to the 19

20 concentration in soil pore water by a chemical s octanol water partition coefficient. Briggs et al. (1982, 1983) assumed that uptake occurred only by chemical absorption during transpiration the chemical partitioning into plant tissue as the water flows through the root, stem and leaf systems. Environment Agency (2003, in preparation) identified key limitations in applying Briggs et al. (1982, 1983) to naphthalene and it is possible that the approach may over- or under-predict uptake of naphthalene in certain situations: Briggs et al. do not account for uptake across the air leaf boundary. Naphthalene volatilises from surface soils and may be absorbed by plants from the air in the microclimate created close to the ground. Briggs et al. do not consider any mechanisms by which the naphthalene concentration could be reduced, such as by plant metabolism, degradation by other organisms, dilution through plant growth or volatilisation from leaf surfaces during air exchange In applying SGVs that include plant uptake, the assessor may therefore wish to consider determining the availability of naphthalene to plants on a site-specific basis and, where appropriate, undertake further investigation (including the sampling and analysis of fruits and vegetables) where exposure via this pathway is of critical concern. Consumption of fruit is not included within the derivation of SGVs, so should this pathway be considered important on a site-specific basis, the additional exposure should be taken into account by the assessor using consumption rates combined with sampled data The uncertainties in modelling exposure via the intrusion of vapour into buildings are described in R&D Publication CLR10 (Defra and Environment Agency, 2002d) and with particular reference to the Johnson and Ettinger (1991) approach in Environment Agency (2004b, 2004c) Although dermal contact and direct soil ingestion are minor contributors to exposure in the standard scenarios, they are likely to more prominent in scenarios in which the primary pathways are otherwise controlled, for example, where vapour intrusion is managed by building design. Further discussion of these pathways can be found in R&D Publication CLR10 (Defra and Environment Agency, 2002d) and the briefing note on the dermal pathway (Environment Agency, 2004a). 20

21 Mobility of naphthalene in the environment 3.18 Most authorities consider naphthalene to be only moderately mobile in the environment, with the atmosphere being the most likely sink from surface soils (Environment Agency, 2003). The reported range of half-life values in soil and groundwater is wide, from a few days to 765 days under aerobic and anaerobic conditions (USEPA, 1999; Mackay, et al., 2000; Environment Agency, 2002a, 2003) In deriving the SGVs for naphthalene the following specific mechanisms by which it can be lost from soil over time have not been included. It is recognised that these may be important on a site-specific basis and assessors may wish to consider their inclusion as part of a detailed quantitative risk assessment (DQRA): Reductions in amount of contamination in surface soils as a result of volatilisation. This is achieved by using the limited source solution of Johnson and Ettinger (1991) to vapour transport and calculating revised average air concentrations over time 6. Reductions in the amount of contamination in soils as a result of chemical and biological degradation. This is achieved by applying a first-order rate model to the soil concentration and predicting the change in the resulting average soil concentration with time 7. Other considerations including acute exposure 3.20 Guidance on using SGVs in the presence of one or more other contaminants is given in R&D Publication CLR9 (Defra and Environment Agency, 2002c). In general, chemical mixtures are only considered where effects are mediated through the same receptor or where substances act on the same target organ or biological system. In the case of naphthalene, the critical threshold effects are those that act on the liver and kidney, and the blood-forming and pulmonary systems. 6 However, the rates of depletion of naphthalene are slow and a mass-balance based finite-source model may significantly over-predict the average contaminant vapour flux. 7 A key assumption in this approach is that the rate of degradation is first order, that is it depends only on the concentration of contaminant present and is not otherwise limited by other factors such as the availability of micro-organisms and the presence of other sources of organic matter and oxygen. Field observations suggest that in many instances a first-order rate constant can be used to approximate degradation in the field (Environment Agency, 2003). 21

22 3.21 The SGVs presented here apply only to the protection of health from long-term exposure to naphthalene contamination and do not include an evaluation of acute effects or aesthetic considerations. As noted in Defra and Environment Agency (2003), naphthalene is acutely toxic via ingestion, inhalation and dermal contact, with the principal health effects being haemolytic anaemia and liver and kidney toxicity. Defra and Environment Agency (2003) reported a range of symptoms of acute toxicity, including nausea, vomiting, lethargy, ataxia, convulsions and abdominal pain. In extreme cases, ingestion of mothballs has resulted in coma and death with the acute lethal dose in adults reportedly in the range mg kg 1 body weight (Defra and Environment Agency, 2003). Although such levels of exposure are unlikely to occur in assessing land contamination, an assessor who deals with small hotspots of highly elevated concentrations of naphthalene should always consider the potential for acute toxicity. Comparison with other approaches 3.22 It is essential that any comparison between the SGVs presented in Table 3.2 of this report and other approaches, including quantitative criteria, should be informed by reference to the conceptual models behind each set of guidelines and take into account the context within which they are intended to apply. There are a number of reasons why the generic assessment criteria developed in one country may differ from those found in another It is not easy to transpose guidance from one jurisdiction to another and to make comparisons between the various calculated contaminant levels. Such guideline values may have been developed in a different management context, depending on legislation and policy, with different overall objectives 8. There may be subtle but significant differences between the conceptual exposure models that take into account the different ways that people behave between countries and differences in site conditions, such as soil organic matter content, soil type and depth to water table. The characterisation of the critical human receptor may also be quite different, which can have a major impact on the guidelines derived. 8 Such objectives might include intervention values or remediation standards to be applied to different current and future uses. 22

23 3.24 The Interdepartmental Committee for the Redevelopment of Contaminated Land (ICRCL) did not publish trigger concentrations for naphthalene, but for total PAHs (ICRCL, 1987). The threshold concentration for total PAHs for domestic gardens, allotments and play areas was 50 mg kg 1 and the action level was 500 mg kg 1. The principal pathway considered was direct soil ingestion (ICRCL, 1986). Little information is available about the conceptual model implicit in these values and therefore further direct comparison with the new SGVs is difficult A comparison of the SGVs with generic assessment criteria in other countries shows that there is a range of values. A large component of this variation appears to come from differences in policy on the exposure scenarios and the choice of HCVs used The current Dutch guidance sets a human health intervention value (IV) for naphthalene in soil of 603 mg kg 1 (RIVM, 1995; VROM, 2000), which is based on a residential land use and on a HCV of 50 µg kg 1 body weight day 1 via the oral route (RIVM, 1995, 2001). The IV is expressed in terms of a standard soil of 10 per cent organic matter and 25 per cent clay, and RIVM (1995) explicitly recommends that the IV for PAHs should not be corrected for differences in soil organic matter content because of their granular form. At 10 per cent soil organic matter, the SGV for the residential with plant uptake land use would be 66 mg kg 1, which is still ten times lower than the Dutch IV. This is principally the result of more stringent HCVs adopted in the derivation of the SGV (especially for inhalation exposure) and the adoption of life-time averaging in the conceptual model used by the current Dutch IV The Dutch have proposed to replace the human health IV with new serious risk concentration (SRC) guidelines for the protection of human health (RIVM, 2001). In revising their approach they reviewed and updated both the methods used to estimate exposure (the C-SOIL model) and the relevant HCVs. The proposed SRC for naphthalene at 10 per cent soil organic matter is 870 mg kg 1 based on an oral HCV of 40 µg kg 1 body weight day 1 (no tolerable air concentration in air is derived). No explanation is provided for the increase in SRC with a decrease in oral TDI (RIVM, 2001) although it may relate to the adoption of the Trapp and Matthies (1995) model to estimate plant uptake. This is more than a factor of ten higher than the SGV for the residential land use, at 10 per cent soil organic matter, for the possible reasons identified earlier. 23

24 3.28 The USEPA currently has soil screening levels (SSL) for 13 PAHs, including naphthalene (USEPA, 1996, 2001). The SSLs were developed to help standardise and accelerate the evaluation and cleanup of contaminated soils at sites on the National Priorities List (NPL) with anticipated future residential land use scenarios. The original SSL for naphthalene is 3100 mg kg 1, taking into account only exposure via direct soil ingestion by a child aged 0-6 years in a residential setting (USEPA, 1996, 2001). The USEPA applied an oral reference dose of 40 µg kg 1 body weight day 1 (USEPA, 1996, 2001). No inhalationbased SSLs were derived because of a lack of supporting toxicological data USEPA (2001) proposed a revised residential SSL of 1100 mg kg 1, with the reduction attributed to the tightening of the oral reference dose to 20 µg kg 1 body weight day 1 and the inclusion of dermal exposure. In addition, an inhalation-based residential SSL of 170 mg kg 1 was derived based on outdoor exposure to vapour and a reference concentration of mg m 3 (USEPA, 2001). USEPA (2001) also put forward SSLs for the indoor and outdoor commercial worker of and mg kg 1, respectively, for exposure via direct soil ingestion and dermal contact, and an inhalation SSL for the outdoor worker of only 240 mg kg It is difficult to compare the SGVs in this report directly with the SSLs because the SSLs apply only to individual pathways. However, for comparison, if the CLEA model was used to derive a UK equivalent to the SSL for the residential scenario (using UK defaults for all exposure characteristics and HCVs) the value for direct soil ingestion and dermal contact would be about 1350 mg kg 1. This is very similar to the corresponding residential SSL proposed by USEPA (2001). 24