Bioaccumulation of Polyhalogenated Carbazoles and Its Related Compounds from Soil to Plant: Impact Factors and Uptake Pathways

Abstract

Polyhalogenated carbazoles (PHCZs) are a kind of emerging compounds that have attracted attention because of their ubiquity, resistance to biodegradation, and toxicities. But little is known about their contamination and bioaccumulation in plants. In this study, bioaccumulation of 11 PHCZs, carbazole (CZ) and benzocarbazole (BZCZ) from soil to plant was investigated by paired soil-earthworm samples from Hangzhou, China and a laboratory bioaccumulation test. ∑₁₁PHCZs, CZ, and BZCZ in herbs were 1.9–247.1 ng/g dry weight (dw), < LOQ–6.1 ng/g dw, and not detectable–265.2 ng/g dw, respectively. The cos θ parameters (above 0.8) support the similarity of PHCZ patterns between soil and plant, which suggests the importance of soil-related uptake into plants. The Kruskal–Wallis H test (p > 0.05) and cos θ (0.706–0.998) indicated a lack of species-specific distribution. The bioconcentration factors (BCFs) for CZ, BZCZ, and PHCZs were 0.21, 3.62, and 0.08–10.52, respectively. 2,3,6,7-tetrachlorocarbazole, 2,7-dibromocarbazole, and 1,3,6,8-tetrabromocarbazole (1368-BCZ) are bioavailable in herbs, whereas CZ and 3-bromocarbazole are not. The negative correlations between BCFs and soil concentrations provide evidence of a kinetic limitation of accumulation at higher exposure levels. The correlation analysis indicated the potential influences of K_OA and K_OW on the transfer of PHCZs from soil to plants. The laboratory test indicates the bioaccumulation of 3,6-dicholorcarbazole and 1368-BCZ from soil to plant and the contribution of soil-root pathway based on the soil-tissue bioconcentration factors. The mass balance model suggests a predominance of the soil-root-leaf pathway compared to the soil-air-leaf pathway. PHCZs with log K_OW > 5 and log K_AW close or < − 6 would be hard to enter the plant via soil-related pathways. The big deviations between C_R/C_{L modeling} and C_R/C_{L motinoring} or BCF_modeling and BCF_monitoring may due to the limitations/uncertainties of the model and the presence of other input pathways. This study provides first evidence of the enter of PHCZs in terrestrial food webs via vegetation.