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Due to its ubiquity and carcinogenicity, the geochemical behavior and health risks of arsenic (As) have been a research focus worldwide. A comprehensive investigation was conducted on the contamination and ecological and health risks of As in the Zijiang River (ZR)-a natural water source. The concentration ranges of As were separately 1.36–6.23 μg/L, 11.42–74.53 mg/kg, and 1.26–130.68 μg/L in surface waters (dissolved), sediments, and pore waters. The concentrations of As in the midstream pore waters and sediments were relatively high, which was related to mining, dam interception, and sediment resuspension. The Monte Carlo simulation results showed that the occurrence probability of As contamination and static risk in sediments was low, however, in the midstream, the secondary risk caused by the release of As should be given more consideration. In the sediments, the transformation paths and the dynamic risk of As were explored based on the delayed geochemical hazard model, showing that there was a probability of a potential burst of 26.47% − 55.88% in the sediments of the ZR. Although at the detected surface waters, the total risk of the noncarcinogenicity and carcinogenicity of As were low, overall adults have lower health risks than children, and As exposure in children should be of concern. This study complements the further understanding of the geochemical behavior of arsenic, which can be extended to other toxic metal(loid)s.

The delayed geochemical hazard (DGH) model was used to show that environmental pollution risk from Pb is a dynamic process as opposed to static. The DGH model describes the potential transformation and release of Pb partitioned in the different fractions of the soil that may be inert but becoming reactive when the conditions of the soil such as pH, moisture, and organic matter become favorable or when the Pb deposited into the soil exceeds the soil-holding capacity. As opposed to single extraction procedures that investigate the total amount of Pb deposited into shooting range soils, irrespective of whether that Pb is from inert or labile Pb species, the DGH model takes into consideration the mineralogical state of the Pb species and the ever-changing physicochemical characteristics of the soil. The total concentration of Pb does not give details on the bioaccessibility, bioavailability, mobility, and quantitative environmental pollution risk of deposited Pb to biota. This model was applied on a case study in shooting range soils highly polluted with Pb at concentrations of up to 38 406.87 mg/kg. The findings indicated that TAB shooting range located inside a military airbase in the southern part of Botswana may be classified as high-risk area of Pb DGH with over 65% of Pb capable of being transformed into the mobile and bioavailable chemical forms. [ABSTRACT FROM AUTHOR]

[Display omitted] • As concentrations in river water, sediment and pore water were studied. • Highest concentration of As in the sediment and pore water was found in the midstream. • Low static and moderate dynamic risks in sediments of the Zijiang River. • The simulated health risks of As in the surface water of the Zijiang River were low. • Reservoir promoted the accumulation and dynamic release of As in the midstream. Due to its ubiquity and carcinogenicity, the geochemical behavior and health risks of arsenic (As) have been a research focus worldwide. A comprehensive investigation was conducted on the contamination and ecological and health risks of As in the Zijiang River (ZR)-a natural water source. The concentration ranges of As were separately 1.36–6.23 μg/L, 11.42–74.53 mg/kg, and 1.26–130.68 μg/L in surface waters (dissolved), sediments, and pore waters. The concentrations of As in the midstream pore waters and sediments were relatively high, which was related to mining, dam interception, and sediment resuspension. The Monte Carlo simulation results showed that the occurrence probability of As contamination and static risk in sediments was low, however, in the midstream, the secondary risk caused by the release of As should be given more consideration. In the sediments, the transformation paths and the dynamic risk of As were explored based on the delayed geochemical hazard model, showing that there was a probability of a potential burst of 26.47% − 55.88% in the sediments of the ZR. Although at the detected surface waters, the total risk of the noncarcinogenicity and carcinogenicity of As were low, overall adults have lower health risks than children, and As exposure in children should be of concern. This study complements the further understanding of the geochemical behavior of arsenic, which can be extended to other toxic metal(loid)s. [ABSTRACT FROM AUTHOR]

The distribution characteristics of mercury fractions at the site near a pesticide plant was investigated, with the total mercury concentrations ranging from 0.0250 to 44.3 mg kg −1 . The mercury bound to organic matter and residual mercury were the main fractions, and the most mobile fractions accounted for only 5.9%–9.7%, indicating a relatively low degree of potential risk. The relationships between mercury fractions and soil physicochemical properties were analysed. The results demonstrated that organic matter was one of the most important factors in soil fraction distribution, and both OM and soil pH appeared to have a significant influence on the Fe/Mn oxides of mercury. Together with the methodology of partial correlation analysis, the concept and model of delayed geochemical hazard (DGH) was introduced to reveal the potential transformation paths and chain reactions among different mercury fractions and therefore to have a better understanding of risk development. The results showed that the site may be classified as a low-risk site of mercury DGH with a probability of 10.5%, but it had an easy trend in mercury DGH development due to low critical points of DGH burst. In summary, this study provides a methodology for site risk assessment in terms of static risk and risk development. [ABSTRACT FROM AUTHOR]

A concept of delayed geochemical hazard (DGH) was proposed instead of chemical time bomb to represent an ecological and environmental hazard caused by sudden reactivation and release of long-term accumulated pollutants in soil/sediment system due to the change of physicochemical conditions or the decrease of environmental capacity. A DGH model was also established to provide a quantitative tool to assess and predict potential environmental risk caused by heavy metals and especially its dynamic evolutions. A case study of DGH was carried out for a mercury-polluted area in southern China. Results of soil column experiment showed that DGH was directly resulted from the transformation and release of pollutant from the releasable species to the active ones through a mechanism of chain reaction. The most possible chain reaction was summarized as Hg E+C+F+O+R → Hg E+C+F+O → Hg E+C+F → Hg E+C → Hg E . Although 8.3% of the studied area with the total releasable content of mercury (TRCP Hg ) exceeded the DGH critical point value of 16.667 mg/kg, with the possibility of DGH burst, the area was classified as low-risk of DGH. This confirmed that DGH model could contribute to the risk assessment and early warning of soil/sediment pollution. [ABSTRACT FROM AUTHOR]

Based on the transformation among metal fractions defined by the Tessier sequential extraction procedure and integrated risk information assessed by delayed geochemical hazard (DGH) methodology, including development paths and their burst probabilities, trigger conditions, and the contribution of each metal to risk development, an approach was proposed to provide an early warning on risk development in metal compound-contaminated sites and tested in a lead and cadmium-contaminated site. Risk assessment indicated that the site was at a high to extremely high ecological risk. DGH analysis revealed that the transformation from the fraction bound to carbonate and organic matter to the exchangeable fraction was dominant in the development of either single or combined lead and cadmium risk, which was triggered by soil acidification and the continuous decline of soil organic matter; risk development might have occurred in 6.52–80.4% of the case site with burst probabilities of 6.52–80.4%, 8.70–39.1% and 8.70–80.4% for lead risk, cadmium risk and combined lead-cadmium risk, respectively; with the dominant role of lead, the two metals overall accelerated the development of their compound risk by changing each other's DGH paths. The proposed DGH-based approach is promising for early warning on risk development in compound contaminated sites. [Display omitted] • A DGH-based method warning the compound risk development was proposed and verified. • DGH paths from bound to carbonate and organic matter to exchangeable was dominant. • The interaction of Pb and Cd overall accelerated the compound risk development. • Soil acidification and organic matter decline triggered the risk development. [ABSTRACT FROM AUTHOR]