Effects of drying pretreatments on the analysis of the mercury fraction in sediments

Tracing and source fingerprinting of metals from the southern coastal sediments in Bangladesh

Trace element pollution from anthropogenic sources is increasingly widespread. This pollution in terrestrial environments threatens agricultural crop production, while in aquatic environments, it threatens fish cultivation. The contamination of these crucial food sources raises significant concerns regarding food safety, security, and its potential adverse effects on human health. Coastal areas are particularly vulnerable to heavy metal pollution due to their proximity to industrial and urban centres, as well as their susceptibility to contamination from marine sources. In attempting to identify the sources of heavy metals (As, Cu, Cr, Cd, Fe, Hg, Mn, Ni, Pb, and Zn) and measure their contributions, we collected soil samples from thirty sites along the three coastal districts (Patuakhali, Barguna, and Bhola) in Bangladesh. Using atomic absorption spectroscopy, heavy metal concentrations in soil samples were measured and three receptor models (PMF, PCA-MLR, and UNMIX) were applied to detect their sources. Pairwise correlation analysis of metal concentrations in 30 sites across 3 coastal districts showed all possible patterns, including both significant and insignificant positive and negative relationships between different metals, except for As and Hg which did not display any significant relationships with other metals. The concentrations of Cu, Fe, Mn, Ni, and Zn exceed the US-EPA sediment quality standard. The applied PCA-MLR, PMF, and UNMIX models identified several sources of heavy metal contamination, including (i) mixed anthropogenic and natural activities: contribution of 59%, 37%, and 43%, and (ii) vehicle emissions: contribution of 23%, 26% and 29%. The recognized metal sources should be prioritised to avoid the discharge of poisonous pollutants from anthropogenic factors and any possible future exposure. This study's findings have implications for ongoing monitoring and management of heavy metal contamination in coastal environments to mitigate potential health and ecological impacts and can inform policy development and management strategies.

Feasibility of soil and sludge standards for freshwater sediment pollutant determination and quality judgment

The environmental standards of soil and sludge have been typically referenced for freshwater sediment determination and quality assessment, especially in some areas without sediment standards. The feasibility of determination method and quality standard of soils and sludge for freshwater sediment was investigated in this study. Fractions of heavy metals, nitrogen, phosphorus, and reduced inorganic sulfur (RIS) in different type of samples were determined, including freshwater sediments, dryland and paddy soils, and sludge with air-drying (AD) and freeze-drying (FD) treatment, respectively. Results showed fraction distributions of heavy metals, nitrogen, phosphorus, and RIS in sediments markedly differed from those of soils and sludge. Fraction redistributions of heavy metals, nitrogen, phosphorus, and RIS in sediments were observed with AD compared to those treated by FD. The proportions of heavy metals, nitrogen, and phosphorus associated with organic matter (or sulfide) in FD sediments decreased by 4.8-74.2%, 9.5-37.5%, and 16.1-76.3%, respectively, compared to those in AD sediments, while those associated with Fe/Mn oxides increased by 6.3-39.1%, 50.9-226.9%, and 6.1-31.0%, respectively. The fraction proportions of RIS in sediments with AD also sharply decreased. Determination of standard methods for sludge and soil caused the distortion of pollutant fraction analysis in sediment. Similarly, the quality standard of sludge and soil was inappropriate for sediment quality assessment due to the differences in pollutant fraction pattern between sediment and soils/sludge. Totally, soil and sludge standards are inapplicable for freshwater sediment pollutant determination and quality judgment. This study would greatly advance the establishment of freshwater sediment determination methods and quality standards.