Regional pollution and diet drive organohalogen contaminant accumulation in mangrove-settled spiders (Nephila pilipes)

Mangrove-settled spiders play a crucial role in maintaining the ecological balance of mangrove wetlands, yet organohalogen contaminants (OHCs) pose a significant threat to these species. This study evaluated the dietary composition (including 15 insect species) and OHC accumulation in Nephila pilipes, a dominant spider species, across two mangrove habitats, using data from 80 OHCs and quantitative fatty acid signature analysis (QFASA). Dichlorodiphenyltrichloroethane (DDT) accounted for over 50 % of the total OHCs in both spiders and insects, followed by polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), alternative halogenated flame retardants (AHFRs), and hexachlorocyclohexane (HCHs). Biomagnification and trophic magnification patterns of OHCs were consistent across both mangroves, suggesting that spatial variability did not significantly influence overall biomagnification. Carnivorous insects exhibited lower proportions of tetra- and penta-BDEs compared to phytophagous insects but had significantly higher total OHC concentrations. The presence of carnivorous insects, such as the ditch jewel, in the spider diet was negatively correlated with phytophagous insects, such as the common emigrant and tobacco cutworm, suggesting potential niche exclusivity. Spiders from more polluted mangroves accumulated higher OHC concentrations, with carnivorous insects contributing 64.9 ± 3.90 % and 67.9 ± 5.79 % to the total OHC load in Zhuhai and Shenzhen, respectively. The regional differences in OHC concentrations were primarily attributed to higher background pollution levels in Shenzhen rather than dietary composition alone. This study highlights the influence of regional pollution on OHC accumulation in mangrove spiders and underscores the importance of region-specific dietary assessments for accurate pollutant bioaccumulation evaluations.