The chronic toxicity and intergenerational effects of environmental concentration of N-(1,3-dimethylbutyl)-N’- phenyl-p-phenylenediamine (6PPD) alone and the mixture of 6PPD and Zn 2+ to Daphnia magna (Cladocera)

Abstract

N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine (6PPD) and Zn²⁺ extensively used in the manufacturing process of tires, can be frequently detected in freshwater. However, the chronic toxicity of environmental 6PPD concentrations remains uncertain, and the intergenerational effects of single treatment of 6PPD and joint exposure of 6PPD and Zn²⁺ at environmental level are still unknown. In this study, the chronic toxicity and intergenerational effects of environmental concentrations of 6PPD (0.02-20 µg/L) and the mixture of 6PPD and Zn²⁺ (5 µg/L) were conducted based on three-generation bioassays using Daphnia magna. In F0, 6PPD produced a hormesis effect on reproduction of D. magna, and a dose-response relationship was observed for the total number of offspring. In the presence of Zn²⁺, the reproduction toxicity of 6PPD was exacerbated. Across three generations, the degenerative maternal effect was concurrently observed in the 0.02 µg/L 6PPD alone and the combined treatment of 0.02 µg/L 6PPD and Zn²⁺, but the adaptive maternal effect was simultaneously shown in the single and the joint exposures with 20 µg/L 6PPD. However, the grandmaternal effect only occurred in the co-exposure treatment with 20 µg/L 6PPD, suggesting that Zn²⁺ could be capable to stimulate the potential toxicity of 6PPD. Our study would provide the first insight into the intergenerational effects of 6PPD alone and the mixture of 6PPD and heavy metal at environmentally relevant concentrations, and could be conducive to understand the environmental risk of tire-derived chemicals due to the synergistic effect of 6PPD and Zn²⁺ and the delayed toxicity effect across generations.