Prioritizing alternative halogenated flame retardants in mangrove spiders: high maternal transfer toxicity outweighs low environmental burden.

Abstract

Halogenated organic contaminants (HOCs) pose significant ecological risks to mangrove spiders through bioaccumulation via food webs and maternal transfer to spiderlings. However, it remains unclear which specific HOCs pose the most critical intergenerational threats to spider populations. A study of 107 HOCs in spiders (Nephila pilipes) and their prey within South China mangroves revealed that accumulation varied by habitat (Shenzhen > Zhuhai) and life stage (reduced levels in gravid cephalothoraxes). Bio-magnification factors (BMF) exceeded unity for several HOCs, particularly short- and medium-chain chlorinated paraffins (SCCPs/MCCPs; ~ 2.7). Maternal transfer ratios (MTR) ranged from 0.43 to 0.94, peaked for dichlorodiphenyltrichloroethanes (DDTs, 0.74) and exhibited parabolic trends with carbon chain length (peak at C14) and chlorination degree (peak at Cl8). Although alternative halogenated flame retardants (AHFRs) constituted only 0.72% of total HOCs, they displayed the highest hazard quotients (HQ = 7.53) and the maternal transfer toxicity indices (MTTI = 5.35; MTTI/HQ ratio = 0.70), indicating substantial intergenerational risks. The increasing prevalence of AHFRs among regional fauna, combined with their metabolic persistence, highlights an urgent need to incorporate these compounds into environmental monitoring and regulatory frameworks. The newly proposed MTTI framework provides a quantitative basis for prioritizing both legacy and emerging HOCs, thereby guiding congener-specific eco-toxicological research and targeted management strategies aimed at preserving coastal predator-prey dynamics under escalating chemical stress.