Mangrove species act as potential biofilters for legacy organochlorine pesticides: evidence from tissue-specific accumulation in the Zhangjiang Estuary.

Mangrove wetlands can act as potential biofilters and biomonitors for legacy organochlorine pesticides (OCPs), yet the species- and tissue-specific partitioning and retention of OCPs in mangrove systems remain poorly understood. Here, we quantified eleven OCPs (HCB, HCH isomers, and DDTs) in surface sediments and in roots, stems, and leaves of four dominant mangrove species (Kandelia obovata, Aegiceras corniculatum, Avicennia marina, and Sonneratia apetala) from the Zhangjiang Estuary, China, using solid-phase microextraction coupled with GC-MS/MS. Total OCP concentrations were relatively low in sediments (0.17-0.81 ng g-1 dw; median 0.32), but substantially higher in mangrove tissues (0.05-7.50 ng g-1 dw; median 0.83), with a tendency for higher tissue burdens in leaves. Diagnostic ratios suggest primarily historical DDT inputs under mixed aerobic-anaerobic degradation conditions, whereas HCH signatures are consistent with lindane-dominated sources superimposed on aged residues. BCFs revealed clear compound-, tissue-, and species-dependent enrichment. Overall, HCHs and HCB were more enriched than DDT-related residues, with δ-HCH showing the strongest accumulation (BCF up to 74.35), whereas selected DDT congeners could still be highly enriched (e.g., 4,4'-DDT, BCF up to 31.96). Leaves exhibited particularly strong enrichment in some species, exemplified by A. corniculatum (leaf HCB BCF = 17.60; leaf δ-HCH BCF = 74.35), while A. marina showed more pronounced enrichment of DDT-related residues (leaf 4,4'-DDT BCF = 31.96; root 4,4'-DDD BCF = 25.56). Among species, A. corniculatum had the highest overall accumulation capacity across tissues, suggesting the greatest phytoremediation potential, whereas other mangroves provided complementary, compound-specific retention functions. These results highlight mangroves as effective biofilters and useful biomonitors for legacy OCPs in subtropical estuaries.