Bioaccumulation, source identification and ecological risk of PTEs in integrated mangrove-aquaculture system: Optimal...

This study explored pollution traits, bioaccumulation, source apportionment and ecological risks of potential toxic elements (PTEs) in surface sediments from mangrove-aquaculture coupling ponds in Mazhang District, Zhanjiang. Sediment salinity spanned 3.97-23.80 g/kg, and silt constituted the predominant grain-size fraction. Cd exhibited the most severe enrichment, with its mean concentration 6-fold higher than regional geochemical backgrounds; all detected PTEs satisfied the Class I marine sediment quality criteria. Relative to mangrove-free ponds, systems vegetated with 13% Aegiceras corniculatum-Rhizophora stylosa mixed mangroves alleviated bioconcentration of Zn, Cd and analogous PTEs but induced selective Cr mobilization, while As concentrations surpassed regulatory limits in 75% aquatic biota specimens. Integrative PCA and PMF models discriminated five pollution endmembers: As-dominated industrial sources, Hg/Cd/Cu/Ni-enriched industrial-traffic mixed sources, geogenic background sources loaded with Zn, Mn, Pb, Ni, Co and Cr, agricultural sources characterized by Zn, Mn, Pb and Cu, and Cd-specific marine-aquaculture sources, where anthropogenic discharges acted as the dominant contributor. Geo-accumulation indices classified Cd and Zn as slight-to-moderate contaminants. Cd yielded the maximum individual ecological risk factor (97-238), and the average comprehensive risk index (RI) of all ponds was 285.95, indicating moderate ecological risk. Ponds covered by 25% mixed mangroves displayed optimal remediation efficacy, with NPI = 0.92 (slightly polluted), RI = 143.62 (low risk) and PLI = 0.89 (slight). Rational mangrove collocation substantially alleviates PTE contamination primarily through Cd retention, necessitating integrated regulation of industrial, agricultural and mariculture pollutant outputs.