Key results from the risk assessment of Malaysian AHSL 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 PCDD/Fs and PCBs. These chemicals were measured at concentrations marginally greater (up to 3.3 times) than the applicable USEPA environmental quality guidelines.
- The receptors identified at the site were both ecological receptors (fish and terrestrial animals) and humans (workers and residents of local homes).
- Key exposure pathways identified were associated with leachate treatment pond effluent and the sludge material that collects at the edges of the leachate treatment pond. Contaminants in the treatment pond may be subject to the following exposure scenarios
- workers may come into contact with contaminants during handling of dried leachate sludge;
- dried sludge may be subject to wind erosion, followed by exposure to workers and local residents; and
- discharges of effluent from the leachate treatment pond may contain contaminants that accumulate in the aquatic food chain, people eating local fish may be exposed to unacceptable concentrations of contaminants.
- The risk assessment model indicated that exposure to contaminated fish might be the predominant route of exposure for PCBs. However, low resolution chemical analysis was conducted on the fish tissue samples and PCB concentrations in tissue were below the analytical detection limit. Consequently the method detection limit, a large concentration, was used in the calculation of total PCB exposure.
- The fish tissue analysis conducted did not include PCDD/Fs, consequently an estimation of dietary exposure for these contaminants could not be made.
- Toxicity reference values (TRVs) were selected in order to calculate a numerical expression of potential human health risk. The chemicals of potential concern were treated both as carcinogens (PCB + dioxin/furan TEQs) and non-carcinogens (Total PCBs and PCB + dioxin/furan TEQs).
- Of the 12 samples collected at the AHSL site, only the sludge collected at the edges of leachate treatment pond exceeded environmental quality guidelines. Normally, this sample would not be considered as part of a human health risk assessment for a contaminated site. However, two potential exposure scenarios associated with dried sludge were identified in the problem formulation.
- The absence of high resolution analysis of fish tissue made it impossible to rule out the potential of human health risks. However, the data collected thus far do not suggest that AHSL is a POPs hotspot.
- The risk assessment results indicated that the contribution of the other potential exposure pathways (other than the consumption of local fish) to the overall potential risk would be negligible for dioxin/furan +PCB TEQ exposure.
- The risk assessment results indicated that PCBs (based on concentrations of total PCBs) are unlikely to pose significant human health risks.
- The data collected thus far and the scenarios assessed suggest human health risks from POPs is generally low and acceptable. However the exposure pathway via fish accumulation of POPs and consumption by humans may warrant further assessment to resolve uncertainties in this specific risk pathway.
- The risk assessment presented in this report focuses on POPs and therefore does not address potential risks from non-POPs substances such as metals, solvents and petroleum hydrocarbons. Accordingly, a final risk management plan should also incorporate knowledge on non-POPs substances.
- Notwithstanding low risk, good environmental and risk management practices require that POPs substances are managed in ways that contain the material within a safe and stable location and without exposure pathways to receptors, and without uncontrolled release in to the environment.