Assessing and Predicting Effects of Sediment Contamination

Transcription

1 Assessing and Predicting Effects of Sediment Contamination David R. Mount U.S. Environmental Protection Agency Office of Research and Development Mid-Continent Ecology Division, Duluth, MN

2 Why Study Sediments? Biological activity/density much higher in sediment compartment than in the water column (both macro- and micro-organisms) Sediments serve as the ultimate sink for most persistent pollutants introduced into aquatic ecosystems In cases of legacy pollution, sediments are often the source of ongoing contamination

3 Elements of Contaminated Sediment Assessment Approach 1)Methods for Measuring Sediment Toxicity 2)Methods to Predict Toxicity from Chemical Concentrations in Sediment 3)Methods to Assess Effects from Bioaccumulative Toxicants 4)Methods to Diagnose the Cause of Toxicity in 4)Methods to Diagnose the Cause of Toxicity in Field-Collected Samples

4 Genus: Lumbriculus Kind of Organism: Oligochaete What their friends call them: worms

5 Genus: Hyalella, Leptocheirus Kind of Organism: Amphipod What their friends call them: scuds

6 Genus: Chironomus Kind of Organism: Midge What their friends call them: bloodworms

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9 Sediment in exposure chambers

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15 Overview of Freshwater Sediment Toxicity Test Methods 10-day exposures Hyalella azteca and Chironomus dilutus Endpoints of survival and growth Chronic exposures Chironomus: 56-d test, including growth, emergence, fecundity, and df1 survival Hyalella: 28-d sediment exposure, followed by 14-d observation for reproduction Bioaccumulation Lumbriculus: 28-d sediment exposure followed by tissue analysis

16 See USEPA EPA/600/R-99/064 for detailed sediment test procedures (ASTM standard also)

17 Marine Amphipod: Ampelisca abdita

18 Marine Polychaetes Used for Bioaccumulation and Toxicity Testing

19 Elements of Contaminated Sediment Assessment Approach 1)Methods for Measuring Sediment Toxicity 2)Methods to Predict Toxicity from Chemical Concentrations in Sediment 3)Methods to Assess Effects from Bioaccumulative Toxicants 4)Methods to Diagnose the Cause of Toxicity in 4)Methods to Diagnose the Cause of Toxicity in Field-Collected Samples

20 Two General Approaches to Sediment Quality Guidelines (SQGs) Empirically-Derived approaches Assess relationship between chemical concentration and biological i l effects in field sediments Use statistical analyses to identify ranges were toxicity is more or less likely Equilibrium Partitioning (EqP) Approach Has a mechanistic basis in theoretical understanding of contaminant t bioavailability il bilit Focused on cause-effect relationships for specific chemicals

21 Distribution of Toxic and Non-Toxic Sedment Samples As a Function of Cadmium Concentration Cumu ulative Freque ency Effects No Effects ERL ERM AET Cadmium Concentration (ug/g, dry wt) ERL = Effects Range-Low; ERM = Effects Range-Median AET = Apparent Effects Threshold

22 %) Midge Su urvival ( Toxicity of Kepone Different in Adams et al. (1985) Different Sediments 0.09% OC 1.5% OC 12% OC Kepone (ug/g dwt)

23 Shortcomings of Empirical SQGs Site-specific response dependent on composition of sediment and co-occurring contaminants Not causally-based; can t evaluate risk on a chemical-specific basis Don t provide a framework for developing p p g remedial targets

24 Desirable Traits for SQGs Linked to risk from specific chemicals Coherent with underlying toxicology Causal basis Add ff t f di t t i Addresses effects of sediment matrix on bioavailability of contaminants

25 %) Midge Su urvival ( Toxicity of Kepone Different in Adams et al. (1985) Different Sediments 0.09% OC 1.5% OC 12% OC Kepone (ug/g dwt)

26 Kepone Toxicity in Different Sediments Proportional to Kepone in Interstitial Water Midge Su urvival (% %) Adams et al. (1985) % OC 20 15%OC 1.5% 12% OC Kepone in Interstitial Water (ug/l)

27 Partitioning of Organic Chemicals Octanol Octanol Water Water

28 Octanol/Water Partition Coefficient (K OW ) Octanol K OW = C octanol C water Water K OW = 3000 ug/kg 3 ug/l = 1000 L/kg Log K OW = 3

29 Partitioning to Organic Carbon Particle of organic carbon

30 Organic Carbon Partition Coefficient (K OC ) C organic carbon K OC = C water K OC = 3000 ug/kg 3 ug/l = 1000 L/kg Log K. OC Log K OW

31 PCB Distribution in Sediment Sediment Particles Interstitial Water

32 Kepone Toxicity in Different Sediments Proportional to Kepone in Interstitial Water Midge Su urvival (% %) Adams et al. (1985) % OC 20 15%OC 1.5% 12% OC Kepone in Interstitial Water (ug/l)

33 Organic Carbon Normalization Reduces Variability Among Sediments Midg ge Survival (%) Midg ge Survival (%) Kepone (ug/g dwt) Kepone (ug/g OC) Adams et al. (1985) 0.09% OC 1.5% OC 12% OC

34 Equilibrium Partitioning (EqP) Water Column Exposure Equilibrium Partitioning Organism Organism K OC Water Sediment Water

35 EqP Predicts Toxicity for Many Chemicals, Organisms, Sediments % Mor rtality DDT ENDRIN FLUOR KEPONE PHEN ACEN Predicted Sediment TU

36 So How Do I Calculate an SQG? Choose a water column effect benchmark: C water = AWQC C organic carbon We know that: K OC = C water So: C SQG (oc) = K OC *C water = K OC *AWQC

37 What About Metals? Same general principle applies to metals Partitioning of Cu, Cd, Pb, Zn, Ni, Ag in anoxic sediments dominated by binding to sulfides Binding capacity measured as acid volatile sulfide (AVS) Metals measured as simultaneously extracted metals (SEM) If more metal than sulfide (SEM-AVS>0) then ( ) potential for metal toxicity

38 Toxicity of Metals on Dry Weight Basis Varies Widely % Mort tality Cd Cu Ni Pb Zn Dry Wt. Concentration (umoles/g)

39 Toxicity Observed Only When SEM Metal Exceeds AVS % Mor rtality Cd Cu Ni Pb Zn Mix 0 (50) SEM - AVS (Micromoles)

40 No Toxicity When Metals Are Low in Interstitial Water % Mo ortality Cd Cu Ni Pb Zn Interstitial Water Toxic Units

41 Questions/Discussion