Multivariate source apportionment and integrated indexical assessment of heavy metal contamination in northeast Indian wetland sediments and soils.

Notwithstanding the indispensable function of wetlands as environmental sentinels, comprehensive multivariate appraisals of heavy metal contamination and concomitant ecological hazards remain profoundly scarce within biodiverse, understudied regions like northeastern India. This critical knowledge gap persists despite escalating anthropogenic pressures and unique local geochemical conditions that modulate metal dynamics and bioavailability. To address this empirical deficit, an all-inclusive analysis of sediments and soils from 19 representative wetlands, including the Ramsar-designated Loktak Pat, was conducted for seven priority metals (Zn, Fe, Mn, Cu, Pb, Hg, As). Multivariate source apportionment via principal component analysis (PCA) revealed a dominant geogenic/lithogenic influence, with the first PC (PC1) accounting for 67.5% and 67.3% of variance in sediments and soils, respectively. This was evidenced by substantial loadings for Fe, Mn, Cu, Pb, Hg, and As. A secondary, less consequential component (PC2; ~ 14% variance) exhibited elevated Zn contributions, intimating potential but limited anthropogenic enrichment. A suite of sophisticated indices, geo-accumulation (Igeo), enrichment factor (EF), contamination factor (CF), pollution load index (PLI), and integrated ecological risk index (RI) collectively demonstrated low pollution states (PLI < 1, Igeo < 0) and negligible ecological risk (RI < 150). Modified hazard quotient (mHQ), toxic risk index (TRI), and hazard index (HI) assessments further confirmed insignificant non-carcinogenic risks to adjacent human populations (HI < 1). Enrichment factors for most metals were < 3, affirming minimal anthropogenic derivation, with the singular exception of localized Cu enrichment (EF 20-22) at sites like Pumlen Pat and Loktak Pat, which may be linked to legacy agricultural phosphate fertilizers or catchment erosion of mineralized soils. This enrichment did not, however, translate to elevated integrated risk. This integrative study confirms that these wetlands are presently low-risk systems for heavy metal pollution. The pronounced geogenic variance structure indicates anthropogenic activities have not substantially perturbed regional metal cycles. These findings accentuate the utility of multi-index frameworks, providing an indispensable baseline for conservation. Sustained, high-resolution monitoring, augmented by isotopic tracking, is unequivocally recommended to preemptively safeguard these vital ecosystems.