Analysis of heavy metal sources and potential ecological risk assessment of mangroves in Aojiang Estuary

Mangrove wetlands are facing increasing challenges from coastal human activity, and heavy metals are common toxic and non-degradable environmental pollutants that accumulate in living organisms. They can accumulate throughout the food chain and pose threats to human health and the ecology. Therefore, taking mangroves in the Aojiang Estuary, where human activity is frequent, this study used geoaccumulation index (I_geo) and potential ecological risk (RI) assessment to assess the degree of heavy metal pollution in mangrove sediments and used the positive matrix factorization (PMF) model to analyze the heavy metal sources. The geoaccumulation index indicated that the mean value of Hg fell within the range of uncontaminated to moderately contaminated, with a few sampling sites classified as moderately contaminated. Cd contamination was classified as moderate, whereas the contamination levels of the remaining elements were generally lower, either uncontaminated or uncontaminated-to-moderately contaminated. Notably, Cu reached its maximum value at the moderately contaminated level at one site. The results of the RI assessment were similar, with Cd pollution categorized as considerable, Hg pollution as moderate, and the remaining pollutant elements as low. The PMF model was used to analyze the four primary heavy metal sources. Hg enrichment is primarily from industrial sources represented by papermaking and printing, whereas Pb, Ni, Zn, and Cu enrichment is from integrated shipping transportation and traffic emission sources, and the low content of Zn, Ni, Co, and other elements indicates that it is a natural source. Cd enrichment is typically derived from agricultural sources driven by fertilizer usage and livestock manure.