N-Nitrosamine Contamination in the Pearl River Delta, China: Concentrations, Toxicity, and Ecological Risks

Abstract

N-nitrosamine contamination in aquatic environments is a global problem; however, there have been few studies on the toxicity mechanisms of different N-nitrosamines in aquatic organisms, especially their combined toxicity at low concentrations. In this study, nine N-nitrosamines were investigated in 16 surface waters in the Pearl River Delta. Four commonly detected N-nitrosamines, N-nitrosodiethylamine, N-nitroso-di-n-propylamine, N-nitrosopyrrolidine, and N-nitrosodibutylamine, were selected to study their toxic mechanisms (growth inhibition and physiological and biochemical changes) when used individually or in combination to Selenastrum capricornutum. The results showed that the total N-nitrosamine concentrations ranged from 27.0 to 727.6 ng/L (mean of 220.8 ng/L) and the four N-nitrosamines and their mixtures inhibited algal growth and the order of toxicity after four days of exposure was N-nitrosodiethylamine > N-nitroso-di-n-propylamine > and N-nitrosodibutylamine > N-nitrosopyrrolidine. The four N-nitrosamines and their quaternary mixtures induced different levels of superoxide dismutase and catalase activity in algae. In addition, malondialdehyde levels increased upon exposure to N-nitrosamine, whereas the opposite was true for total protein and photosynthetic pigments. Concentration addition and independent action models indicated that the quaternary mixtures exhibited an additive effect on algal toxicity and showed significant inhibition (up to 15.6%) at actual environmental concentrations (1 μg/L). The risk quotients for N-nitrosamines modeled using ECOSAR were significantly overestimated compared with the experimental toxicity data. Risk assessments using the levels of N-nitrosamines in the Pearl River Delta showed that the risk quotients were all below 0.1 but the ecological risks due to N-nitrosamines in the form of mixtures would be underestimated. A small number of environmental concentration measurements in wastewater and receiving water from other studies suggest that the potential risk of N-nitrosamines to aquatic life cannot be excluded.

Keywords: N-nitrosamines, quaternary mixtures, selenastrum capricornutum, growth inhibition, Toxic mechanism, Risk quotients