The assessment of contaminated sediments from mining activities using a sediment decision-making tool

Transcription

1 The assessment of contaminated sediments from mining activities using a sediment decision-making tool Rachael Fletcher 1 and Paul Welsh 2 Ontario Ministry of the Environment 1 Environmental Monitoring and Reporting Branch 2 Standards Development Branch

2 Decision-making Framework Underlying philosophy of the approach to sediment assessment is that observations of elevated concentrations of contaminants alone are not indicators of ecological degradation 2

3 Decision-making Framework Based on ecological risk assessment principles Sufficiently prescriptive to standardise the decisionmaking process, while acknowledging the influence of site specific conditions Uses 4 lines of evidence (LOE): 1. Sediment chemistry 2. Biomagnification potential 3. Sediment toxicity 4. Benthic invertebrate community structure 3

4 Decision-making Framework 9-step process: Step 1 Examination of available data Step 2 Sampling and analysis Step 3 Potential risks based on contaminant concentrations Step 4 Potential for biomagnification Step 5 Sediment toxicity Step 6 Benthic community composition Step 7 Decision matrix Step 8 Further assessment Step 9 Deeper sediments 4

5 Sudbury mining The Sudbury area has a long history of mining activities, which began in 1883 when copper ore was first discovered in the area. Currently the primary metal extracted is nickel, but copper, zinc, and to a lesser extent cobalt have also been extracted from the rocks in this area. A large number of mines have or continue to operate in the area. Metal contamination of the surrounding area has been documented since the 1960 s. Since the 1970 s considerable effort has been undertaken by 5 the mining companies to control metal discharges to Junction Creek.

6 Junction Creek Junction Creek flows southwest through the city of Sudbury. Much of the area drained by Junction Creek is within the zone of atmospheric deposition from the mining and smelting operations. The study was undertaken to address the impacts to the creek from a variety of sources existing in the area, and the relative contribution of each. 6

7 Steps 1-3: Initial Screening Assessment Surficial Sediments STEP 1 Examine available data STEP 2 Develop, implement SAP, assess COPC Decision 1 Toxicity OR biomagnification possible? no No management actions required STEP 3 yes Compare to reference conditions Decision 2 Any COPC > reference +20% and significantly different no No management actions required 7 Taken from Chapman & Anderson, 2005 yes

8 Step 1: Examine Available Data Before any sampling was undertaken, all the available background information was reviewed. On the basis of this data, the study area was defined. 8

9 Step 2: Sampling and Analysis Plan Based on findings from Step 1, a SAP was developed Sampling strategy was chosen which considered stations located in relation to specific sources (Deterministic strategy). Sampling locations were chosen to ensure all routes to the receiver were considered Sediment, water, biota and toxicity were considered 9

10 Copper in sediment (ug/g) SEL = 110ug/g 10

11 Nickel in Sediments (ug/g) SEL = 75ug/g 11

12 Steps 4-6: Quantitative assessment STEP 4 Model biomagnification potential STEP 5 Decision 3 Biomagnification a potential concern? yes/no Assess sediment toxicity Decision 4 Sediments toxic? STEP 6 yes/no Compare to reference conditions Decision 5 Benthic assessment Appropriate/ Possible? 12 Taken from Chapman & Anderson, 2005 yes/no

13 Step 4: Potential for biomagnification Biomagnification assessed through: Fish collections (young-of-year) Fish tissue concentrations from fathead minnow bioassays 13

14 Potential for biomagnification In situ young-of-year fish collections (means) [ug/g] Fathead tissue residue from bioassays [ng/g] wet weight Fathead Minnows Copper Nickel Yellow Perch 10 Pre-exposure Control 0 Timmins RamseyMcCharles Mud Simon Sampled Lakes Station Nickel L-2 Copper 21 14

15 Step 5: Assess Sediment Toxicity Determines direct toxicity (acute and chronic) using field-collected sediments. Three different organisms were used: Mayfly Chironomid Fathead minnow 15

16 Organism Mortality in Sediment Bioassay Tests % Mortality Control L-2 21 Station Mayfly 16 Chironomid Fathed minnow

17 Organism Growth in Sediment Bioassay Tests 30 mg wet weight Control L-2 21 Station Mayfly Chironomid 17

18 Fathead Minnow Tissue Residues [ng/g] wet weight Station Nickel Copper 18

19 Step 6: Benthic Community Structure In some areas where there is the possibility of high disturbance, the assessment of sediment dwelling organisms may not be possible. The assessment of benthic community structure in Junction Creek was possible and considered an important line of evidence 19

20 Step 6: Benthic Community Structure Can be considered as long term in situ bioassays (multigeneration tests). Benthic community typically dominated by chironomids and oligochaetes 100% Density and diversity reduced below mining/smelting Some increased density at a few locations (d/s STP) proportion of key organisms 80% 60% 40% 20% 0% 3 1 % Mollusca % Chironomidae % Oligochaeta A 6-B L-4 16 L-5 L-2-B L-6 L-8 L-9 20

21 Summary Step 3 Potential risks based on contaminant concentrations - All of the metals that exceeded criteria in are associated with potential toxic effects. Step 4 Potential for biomagnification - Young of the year fish showed uptake of metals such as arsenic, nickel and copper in Mud Lake and Simon Lake. - Fish were not obtained from Kelley Lake Step 5 Sediment toxicity - Laboratory sediment bioassays showed significant lethality in sediments from Kelley Lake and d/s Copper Cliff - There was growth impairment in both chironomids and mayflies in Nolins Creek - There were no adverse effects on fathead minnows. Step 6 Benthic community composition - Biological impacts on the benthic community only observed below mining/smelting 21 sites (reductions in density and diversity sometimes severe)

22 Step 7: Construct Decision Matrix Based on ranking data from the available lines of evidence (sediment chemistry, toxicity, benthos and biomagnification potential) Weight-of-evidence (WOE) approach taken Site-by-site basis At this stage of the framework, a definitive final decision may be possible 22

23 Step 7: Construct Decision Matrix Site Sediment Chemistry Biomagnification Potential Toxicity Benthos Alteration a Assessment * * JC03 (REF) Fully assess risk of biomagnification Determine reasons for benthic alteration and JC08 fully assess risk of biomagnification Determine reasons for benthic alteration and JC11 fully assess risk of biomagnification JC12 Management action required Determine reasons for benthic alteration and JC16 fully assess risk of biomagnification JC21 Management action required JC-L2 Management action required a Benthos alteration may be the result of other factors, either natural (e.g., competition/predation, habitat differences) or human-related (e.g., water column contamination) (Chapman and Anderson 2005) Adverse effects likely Ο Adverse effects may or may not occur Adverse effects unlikely 23

24 Conclusions Based on the Decision Making Framework outlined which uses the rule-based, weight-of-evidence approach, further action is advised for JC12, JC21 and JC-L2 and the risk of biomagnification and reasons for benthic alteration need to be fully assessed for the remaining sites assessed in the matrix Not all sites sampled were presented in this scenario, and not all lines of evidence were available for review. These sites may require additional monitoring to assess laboratory toxicity and/or bioaccumulation potential 24

25 Integration of the Framework The ministry has integrated the framework into its own sediment assessment and management procedures. The new integrated document incorporates the two existing MOE documents (MOE Guidelines for the Protection and Management of Aquatic Sediment Quality in Ontario, and MOE An Integrated Approach to the Evaluation and Management of Contaminated Sediments) for the assessment and management of sediments with a new MOE/Environment Canada Framework so that practitioners now have all relevant MOE information in one document. The integrated document is a stand-alone MOE document for assessing and managing contaminated sediments, and will update and replace the existing 1993 and 1996 documents. 25

26 More Information An overview of the framework is provided in: Chapman, P.M. & J. Anderson, A decision-making framework for sediment contamination. Integrated Environmental Assessment and Management. Vol. 1 (3):