Site-specific water quality criteria for aquatic ecosystems: A case study of pentachlorophenol for Tai Lake, China

Given the widely varying types of aquatic ecosystems and bioavailability of chemicals, it is important to develop site-specific water quality criteria (WQC) to ensure criteria are neither over- nor under-protective. In the study, using pentachlorophenol (PCP) as an example, several approaches to derive site-specific WQC were investigated, including the conventional species sensitivity distribution (SSD), weighted SSD based on the proportion of each trophic level, and water effect ratio (WER) method. When corrected to a pH of 7.8, the conventional SSD approach resulted in criteria maximum concentration (CMC) and criteria continuous concentration (CCC) of 18.11 and 1.74 μg/L, respectively. If SSD was weighted according to the current species composition in Tai Lake, the CMC and CCC were 32.81 and 4.48 μg/L, respectively. However, available data suggest that many sensitive species inhabiting Tai Lake during 1980s were disappeared. Considering the species composition of the healthier ecosystem in 1980s, the CMC and CCC were 10.99 and 0.38 μg/L, respectively, which provide more protective water quality standards. Water effect ratio (WER) was further used to correct for co-occurrence of other toxicants and factors affecting bioavailability of PCP. A final WER of 4.72 was applied to adjust the criteria derived by using the weighted SSD for the 1980s aquatic community, and the final CMC and CCC obtained were 51.87 and 1.79 μg/L, respectively, at a pH of 7.8. Water quality criteria derived using the 1980s species composition and adjusted with WER were deemed the most appropriate WQC for water management and aquatic life protection. Merits of the various approaches for developing WQC for protection of aquatic species were discussed.