Assessing heavy metal pollution levels and associated ecological risks in peatland areas in the Mekong Delta region

Heavy metal (HM) pollution in soils and sediment is a significant concern, yet its levels and ecological risks in peatland areas remain unexplored. This study evaluates these aspects in three peatland regions of the Long An province in Vietnam. Comparisons of HM concentrations in peatland sediments from Tan Thanh, Thanh Hoa, and Duc Hue provinces in the study locations revealed highest values in the Tan Thanh region. Specifically, Cu and Ni were found in sediments at levels two to three times higher than the threshold effects level (TEL) and the effects range median (ERL) guidelines. The main sources of HM pollution in the study area are predicted to include the production and use of fertilizers and pesticides, metal surface processing, mechanical engineering and electronics manufacturing, and chemical plants. Further, positive correlations between HM concentrations and factors such as pH, total organic carbon (TOC), and clay-silt ratio in the sediments were identified through Spearman correlation analysis. The results obtained from the correlation analysis were further corroborated by Bayesian network analysis, which was also applied in this study. In addition, the contamination factor (CF) index indicated that Ni has a pollution level of "moderate degree" in Thanh Hoa (CF = 1.3) and "considerable degree" in Tan Thanh (CF = 3.2), whereas, Cu has a pollution level of "moderate degree" in both Thanh Hoa (CF = 1.3) and Tan Thanh (CF = 2.4). The modified degree of contamination (mCd) ranked the areas as Tan Thanh > Thanh Hoa > Duc Hue, with mCd indexes of 1.3, 0.7, and 0.4, respectively. The potential ecological risk index (RI) indicated a "low risk" level, with an average RI of 35.6 across all sites. These findings address knowledge gaps in HM pollution in peatlands but also contribute to the development of strategies for the protection of peatlands.