Levels of bioavailable manganese in river sediment may elevate reproductive risk in model organism Caenorhabditis elegans.

Manganese occurs naturally in sediment, yet anthropogenic sources, such as industrial wastewater and mining, increases Mn concentration. However, the environmental risk of bioavailable Mn is often overlooked and infrequently addressed. A probabilistic risk assessment was conducted to determine the effects of bioavailable Mn in river sediments on reproduction in model organism Caenorhabditis elegans using in utero egg counts and germline apoptosis as biomarkers. The lowest-observed-adverse-effect level (LOAEL) of sediment Mn that decreases in utero egg counts or increases germline apoptosis in C. elegans was 50 or 10 mg of Mn(II) per kg of dry weight sediment, respectively. Effect and exposure analyses were conducted using Hill model-simulated concentration-response curves and Mn concentrations of Laojie River sediment. Risk quotients (RQs) and exceedance risk (ER) analyses showed that bioavailable levels of Mn in Laojie River sediments from downstream sites collected during the dry season elevate reproductive risk as measured by germline apoptosis. These findings suggest that bioavailable levels of Mn in sediment exert negative impacts, and germline apoptosis is a sensitive biomarker for reproductive risk assessment. Our results also suggest that the anthropogenic Mn pollution in river sediment and spatial-seasonal bioavailability of Mn should be considered to improve sediment quality control.

The bioavailability and potential ecological risk of copper and zinc in river sediment are affected by seasonal variation and spatial distribution.

River sediment is the ultimate sink for heavy metal pollution. Copper (Cu) and zinc (Zn) are consistently found at environmentally significant levels in sediments worldwide. We hypothesized that the bioavailability and potential ecological risk of Cu and Zn in river sediments may be affected by seasonal variations and spatial distribution. In this study, we tested our hypothesis using highly industrialized river sediments (Laojie River) as an example. The concentration of heavy metals, pollution indexes, and risk indexes were evaluated and multivariate statistical analyses were performed. We found that seasonal variations affect heavy metal contamination, pollution indexes, and potential ecological risk in sediments and this effect was more severe in the dry season. In addition, higher levels of metal contamination, pollution indexes, and potential ecological risk were observed midstream and downstream of the Laojie River. We found that Cu and Zn were the primary contaminants in Laojie River sediments and may originate from common anthropogenic sources. Analysis of the chemical fractions further revealed that Cu and Zn exhibited high mobility and potential bioavailability risk. In addition, a high percentage and amount of Cu and Zn were found in exchangeable fractions, suggesting they pose a great risk to aquatic organisms. Our results indicate that seasonal variations and spatial distribution affect the bioavailability and potential ecological risk of Cu and Zn in river sediments. These findings suggest that seasonal variations and spatial distribution are important parameters to consider for environmental monitoring and environmental management in aquatic environments.