Biology Factors Modifying Contaminant Effects

Transcription

1 Biology 5868 Factors Modifying Contaminant Effects

2 Modifying Factors Any characteristic of the organism or its surrounding environment that affects toxicity of a pollutant is considered to act as a Modifying Factor (adapted from Rand & Petrocelli 1985). Biotic Modifying Factors (studied less) Abiotic Modifying Factors (studied more)

3 Biotic Modifying Factors (Applicable to the Receptors) Organisms Prokaryotic vs. Eukaryotic, Plants vs. Animals, Aquatic vs. Terrestrial, Vertebrates vs. Invertebrates Daphnia magna vs. Daphnia pulex. Life Stage Embryos vs. Larvae vs. Juveniles vs. Adults, Seeds vs. Seedlings, Molting vs. Non molting Phase, Reproductively Active vs. Non reproductively Active.

4 Biotic Modifying Factors (Applicable to the Receptors) Body Size The following relationship applies for acute lethality: LC (or D) 50 = a W b W = weight of the organism b = slope of the LC 50 vs. weight line. a = intercept of the LC 50 vs. weight line. Values for a and b are determined experimentally. Literature shows b values to be ~ 0.7. Organism Condition Nutrition, Parasitism and Overall Health (all influenced by acclimation phase)

5 Biotic & Abiotic Modifying Factors (Applicable to the Contaminants) U.S. EPA Office of Pesticide Products & Toxic Substances (OPPTS) requires that specific environmental fate data be submitted by chemical manufacturers/registrants. Biodegradation: The breakdown of chemicals by the metabolic processes of microbes. Hydrolysis: The introduction of HOH or OH into an organic molecule resulting in cleavage of another chemical bond. Photolysis: A sunlight mediated photooxidative degradation process.

6 Biodegradation The least understood of the modifying factors. Lack of understanding is attributable to the number and complexity of the biochemical processes involved (bacteria, protozoans, fungi all contribute). Studies focus on water, soil and sediment, and are conducted under both aerobic and anaerobic conditions. 14 C labeled parent compound is used. A mass balance approach is recommended for water/sediment studies. Rate of mineralization to 14 CO 2 is the key parameter for the soil study. The study conditions are difficult to standardize. Although soil types can be standardized, the associated microbial populations are clearly random variables. These studies are often the most difficult to set up and conduct successfully (see OPPTs handout).

7 Hydrolysis Susceptible Chemicals Include: esters, alkyl halides, epoxides, amides, carbamates and alkyl phosphates. Alkyl Halides Alcohols Esters Acids Epoxides Diols Hydrolysis reactions are dependent on both temperature and ph. The key end point is half life of the parent compound; e.g. the time required for the parent compound to be reduced to half its initial concentration. These are complex studies to conduct (see OPPTs handout).

8 Photolysis 1. Direct Photolysis Sunlight is absorbed directly by the parent compound to form excited or radical species, which then undergo further reactions to form stable compounds. AFFECTS ketones, aldehydes, polycyclic aromatics & aromatic amines 2. Indirect Photolysis Sunlight is minimally absorbed by the parent compound. The parent compound instead reacts with intermediates formed during the photolysis of associated dissolved organic matter (tannic & humic acids). AFFECTS furans, phenols, sulfides and nitro aromatics Studies address water, soil and air. Again, the key parameter is half life of the parent compound. The studies are very complex regarding light quantity & quality (see OPPTs handout).

9 Abiotic Modifying Factors Inorganic Contaminants (metals & metaloids) have been studied extensively. In aquatic systems, including groundwater, their effects are dependent on: Fractionation Metals vary in their extents of bioavailability in sediments or saturated soils. Freely Exchangeable Mineralized Complex

10 Metals Fractionation Figure 4.2 from text

11 Abiotic Factors Modifying Metals Sulfide Content In anoxic sediments, there is an inverse relationship between sulfide content and the bioavailability of Cd, Cr, Pb, Hg, and Ni. Sulfides Metal Availability ( effects) ph In general, there is an inverse relationship between ph and the bioavailability of metals and metaloids in aqueous systems. ph Metal Availability ( effects) Water Hardness The [Ca] and [Mg] ions in water (expressed as mg/l CaCO 3 equivalent). There is a quantitative inverse relationship between water hardness and the bioavailability of Cd, Cr, Cu, Pb, Ni and Zn. Hardness Metal Availability ( effects)

12 Water Hardness & Metals Lethality to Trout From Rand & Petrocelli 1985

13 Abiotic Modifying Factors Organic Contaminants (PCBs, Pesticides, PAHs...) have also been studied extensively. Much of the research on abiotic modifying factors has focused on contaminated sediments. Sediment Quality Criteria should be developed based on specific properties of the contaminants (water solubility & K ow ) and sediments (total organic carbon).

14 Sediment Quality Criteria Constituent K oc FCV (ppb) f oc SQC TCE PCE cis DCE trans DCE Vinyl Chl Constituent Log 10 K ow x Log 10 K oc K oc (antilog of Log 10 K oc ) TCE PCE cis DCE trans DCE Vinyl Chl

15 Abiotic Modifying Factors Figure 4.3 from text

16 Examples of Combined Modifying Factors Phototoxicity as mediated by Chlorophyll Biosynthesis (Biotic) and Light (Abiotic) Photosynthetic Inhibition (Biotic) as influenced by Temperature and Light (Abiotic)

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