Bioavailability, ecological risk assessment and policy implications

Transcription

1 Bioavailability, ecological risk assessment and policy implications Patrick van Beelen (RIVM), Willie Peijnenburg (RIVM) and Megharaj Mallavarapu (CERAR)

2 What I am going to tell you Ecological risk assessment in the European Union Examples of microbial toxicity tests Differences between laboratory tests and field conditions Site-specific risk assessment multi-substances metals Triad approach Pollution Induced Community Tolerance 2

3 Soil quality guidelines determine how stringent measures for waste collection should be Measures for waste collection costs more than 2% of gross domestic product Protection of human health Protection of ecosystems Prevention of further spread of the pollution 3

4 Ecological risk assessment in the European Union Predicted Environmental Concentration PEC fate models predict PEC from emissions chemical measurements are used to calibrate the fate models Predicted No Effect Concentration PNEC Toxicity tests Compare PEC with PNEC 4

5 Sorption influences the PEC Sorption determines partitioning Sorption influences biodegradation Paraquat Polycyclic aromatic hydrocarbons 5

6 Predicted No Effect Concentration (PNEC) PNEC for protection of species For example the earthworm test or microtox test PNEC for protection of processes For example nitrification test PNEC for protection against bioaccumulation Biomagnification factors Select lowest PNEC 6

7 PNEC for protection of processes The microorganisms are usually not separated from the soil Each soil sample has its own microflora Normalization to standard soil with 3.4% OM is not recommended Averaging all the measurements of a single process in different soils is not recommended either Even nitrification is performed by different species in different soils 7

8 Effect of Total Petroleum Hydrocarbons contamination (mg kg -1 ) on soil microflora Megharaj et al. Arch Environ Contam Toxicol 38: (2000) Total C6-C High Med-High 9200 Medium 5200 Med-Low Algae Urease Dehydrogenase Micro-biomass-C 2120 Low Uncontaminated Microbial parameters (%) 8

9 Algal diversity in TPH contaminated soils Algal species composition is a good indicator of pollution Alga Control Contaminated Low Med Low High Chlorella Chlorococcum Scenedesmus Green unicells Ulothrix Anabaena Nostoc Nostoc Phormidium Megharaj et al. Arch Environ Contam Toxicol 38: (2000) 9

10 Effect of Cr on Soil biota: Pore water (1 h saturation) toxicity to algal growth Soil/Contamination Total Cr (µg ml -1 ) Cr (VI) (µg ml -1 ) % algal growth Control 0.07 nd 100 Low Medium High

11 Cr toxicity to alga exposed to porewater from 12 h saturation Soil/ Total Cr Cr (VI) % algal % Cr in the Contamination (µg L -1 ) (µg ml -1 ) growth algal mass Control 0.13 nd 100 nd Low 0.32 nd Medium 0.55 nd High 0.97 nd

12 PNEC is calculated from toxicity tests EC10 can be used instead of NOEC Tests have to be normalized to standard soil with 3.4% organic matter % survival EC50 NOEC EC log toxicant concentration 12

13 Toxicity tests are performed under optimal conditions Healthy well fed organisms without predators, competitors or parasites Sandy soil amended with: water chalk CaCO 3 increases ph and lowers bioavailability of metals dung or fertilizer increases microbial biomass and stimulates biodegradation optimal temperature stimulates biodegradation 13

14 Soil pollution is present under marginal conditions Pollution is present in certain layers and hotspots Soil organisms may be repelled or attracted Conditions for biodegradation are poor Lack of oxygen or other compounds necessary for growth of microorganisms Suboptimal temperatures Soil may be dry or waterlogged Strong sorptionto soil particles Aging changes the bioavailability of pollutants Decrease in ph and organic carbon increases toxicity of metals Increased sorption of organic compounds and metals Changes in the composition of one mixtures of pollutants 14

15 Field populations are quite different from laboratory populations used in toxicity tests Toxicity tests monitor parameters which are easily to measure Survival, growth, reproduction In the field more subtle parameters determine survival Competition, escape from predators, disease resistance, survival under adverse conditions like cold, drought and starvation 15

16 How to calculate PNEC from NOEC or EC10 values Normalize all single species NOEC values NOEC standard soil =NOEC experimental soil 3.4% / x% x = percentage organic matter in experimental soil Divide lowest NOEC with assessment factor PNEC = Lowest NOEC / assessment factor three trophic levels, plants (primary producers), invertebrates (consumers) and microorganisms (decomposers) Information available assessment factor EC50 short-term test 1000 NOEC long-term test 100 NOEC 2 trophic levels 50 NOEC 3 trophic levels 10 16

17 How to calculate PNEC from more than 10 NOEC or EC10 values using statistical methods Normalize all single species NOEC values Take the geometric average of the NOEC values for the most sensitive endpoint of each species. More than 10 different species must have been tested. Logarithmically transform these values in order to get a Species Sensitivity Distribution (SSD) Calculate the mean and standard deviation of the SSD Less error-prone than focusing on the lowest NOEC which might be an outlyer Adding new data or removing low-quality data does not change the SSD much 17

18 Calculation of the PNEC from the SSD Log PNEC = average -1.7 standard deviation 95% of the NOEC values are higher than the PNEC On occasion an extra safety factor ranging from 1 to 5 can be applied according to the European Union guidelines PAF 5% Potentially Affected Percentile of species (%) NOEC (µg.l -1 ) on a log 10 scale HC 5 Env. Conc. (µg.l -1 ) on a log 10 scale 18

19 Site-specific risk assessment Is a change in land use possible? Measure the expected pollutants. Normalize concentrations for standard soil Normalized concentration = concentration 3.4% / x% x = percentage organic matter in soil at polluted site Is there any pollutant which exceeds the European Union quality standards? Does the future use of the site requires ecological functions? 19

20 Site-specific risk assessment Add up Hazard Units ( HU) for pollutants with similar modes of action HU = concentration / geometric average NOEC total HU = Σ HU Calculate Potentially Affected Fraction from normalized concentration and SSD Multiply chances of survival for each mode of action (1-PAF total ) = (1-PAF mode1 ) (1-PAF mode2 ) (1-PAF mode3 ) PAF < 5% clean PAF > 50% dirty in between there is need for refined modeling 20

21 Site-specific risk assessment of metals Metals are present in a site-specific natural background concentration Toxic effects of natural background concentrations are not undesirable These natural background concentrations might have been elevated to a site-specific ambient concentration Low ambient concentrations should not be mistaken for background concentrations 21

22 Site-specific risk assessment of metals In soil metals are oxidized to their cations which sorb to: clay amorphous metal oxides organic material or precipitate with many anions Different metal cations compete to bind on the strongest binding sites or precipitate with anions with the highest affinity Aging of metal pollution can sometimes decrease the extractable fraction but slow decreases of organic matter and ph can also increase that fraction 22

23 Site-specific risk assessment Problems Problems with the bioavailability of metals You are never sure that you have measured all pollutants Solution Triad approach Chemical measurements Toxicity tests Ecological observations 23

24 Site-specific risk assessment Pollution Induced Community Tolerance (PICT) Microorganisms are extracted from soils Exposed to increasing pollutant concentrations in the laboratory Tolerance is measured log EC50 (mg/l) log EC50 (mg/l) Zinc R²= total concentration log mg/kg 3.0 Van Beelen et al. ET&C 11 in press Zinc R²= pore water concentration log mg/l 24

25 Basic scheme site-specific ecological risk assessment 1. description of of actual / desired landuse land-owner RIZA 2a. formulation of site-specific ecological aspects 2b. set up assessment tools land-owner (local) authorities experts remediation soil management timetable 3. site-specific data toxicity chemistry risk effect ecology determination relative risk, hazards, effects experts contamination monitoring acceptable with respect to the landuse contamination unacceptable in future contamination will be acceptable with respect to landuse and measures monitoring 25

26 Conclusions: A crude prediction of the toxicity of mixtures of organic chemicals in soil is possible Chemical measurements are not sufficient for sitespecific risk assessment Additional toxicity tests and ecological observations are necessary 26