Key results from the risk assessment of the Thailand MEA case study are:
- The problem formulation indicated that all the components required for a human health risk were present: chemical hazards, receptors and pathways linking the hazards and receptors.
- The chemical hazards identified were PCBs and PCDD/PCDFs. The receptors identified at the site were both ecological receptors (fish, crabs and snails) and humans (workers and residents of local homes).
- Exposure pathways identified were split into onsite exposures, and exposures related to off-site migration of contaminants via wind erosion or surface water run-off.
- The exposure assessment used a computer-based model to estimate the total daily exposure of people (workers and local residents) to PCB + PCDD/PCDF TEQs. The model indicated that ingestion of contaminated food (e.g., fish) is likely the predominant route of exposure for PCBs and PCDD/PCDFs.
- For the Hazard Assessment, toxicity reference values (TRVs) were selected in order to calculate a numerical expression of potential human health risk. The chemicals of potential concern (PCB + PCDD/PCDF TEQs) were treated both as carcinogens and non-carcinogens.
- Results of the Risk Characterization indicated that there is a potential human health risk associated with exposure to PCBs & PCDD/PCDFs, primarily due to the consumption of fish tissue.
- The potential risk was placed into the context of uncertainties and assumptions made during the risk assessment. Two options were discussed: (1) conducting a refined (more detailed) risk assessment in an attempt to determine if potential risks are actually negligible or absent; or, (2) conduct risk management activities at the site to mitigate potential risks.
Towards Risk Management
The national participants of the National Training Workshop which took place in Hue Hin from January 26th – 27th, 2009 also assessed potential risk management measures that could be applied to reduce the exposure and related human health risks to workers, and local residents. A short list of possible measures was created. Recommended measures included:
- Develop and enforce an occupational health and safety plan;
- Monitor and verify effectiveness of mitigation strategies;
- Risk Communication and Training; and
- Measures for controlling PCB Hazards and controlling off-site Transport of Contaminants – i) Excavate contaminated soils and store this material in a secure storage building in clearly labeled barrels or cap contaminated soils with pavement where excavation is not practical; and ii) Prevent soils from being washed off site with surface water run off. One option is to install catch basins along the inside of the property at drainage pipes. Catch basins should be cleaned out regularly. Collected sediments should be stored on site in a responsible manner.