Use of SSD in China
Chinese Research Academy of Environmental Sciences, China
Species sensitivity distributions are usually used in the development of water quality criteria (WQC) and require a large number of toxicity values to define a hazard level to protect the majority of species. In the present study, we introduced the specific use of SSD in the study of water quality criteria in China. As case studies, WQC for representative water-body pollutants in China using SSD were conducted. i.e. toxicological data for zinc (Zn), cadmium (Cd), hexavalent chromium (Cr (VI)), benzene, and nitrobenzene were collected from various databases, publications and experimental test data. These toxicological data were screened and constructed into SSD curves. WQC for protection of the freshwater aquatic life in China against 5 representative pollutants were then derived. The values derived in this study were compared with those issued by the US Environmental Protection Agency and the Chinese national environmental standard for surface water to identify factors underlying the differences. The results showed that the SSD curves for the 5 pollutants differed significantly, with the examined aquatic species being generally more sensitive to Zn, Cd, and Cr (VI) than benzene and nitrobenzene.
While SSDs based on measured toxicity values can provide a strong level of confidence for environmental protection, there is still some uncertainty in their applicability for untested species. Additionally, SSD development has been limited to a relatively few chemicals because of the requirement for toxicity data for a broad diversity of taxa. Interspecies correlation estimations (ICE) models may provide great assistance for addressing the development of WQC that are protective of species that cannot be tested. To address this need, we also tried to use ICE-based SSD in deriving WQC for zinc in China. Taken zinc for example, ICE-based-SSDs were generated using 3 surrogate species (common carp (Cyprinus carpio), rainbow trout (Oncorhynchus mykiss), and Daphnia magna) and compared with the measured-based SSD and corresponding HC5. The results showed that no significant differences were observed between the ICE- and the measured-based SSDs and HC5s. Given the similarity of SSD and HC5s for zinc, the use of ICE to derive potential water quality criteria for diverse chemicals in China is proposed. Further, a combination of measured and ICE-derived data will prove useful for assessing water quality and chemical risks in the near future. Above all, the comparative study of SSD in WQC studies may offer guideline values for future WQC studies in China.