A field study of the relationship between sulfide-bound metals and bioaccumulation by Limnodrilus sp. in a heavily polluted river

Risk assessment of trace metal-polluted coastal sediments on Hainan Island: A full-scale set of 474 geographical locations covering the entire island

Hainan Island is the second largest island and one of the most famous tourist destinations in China, but sediment contamination by trace metals in coastal areas is a major issue. However, full-scale risk assessments of trace metal-polluted coastal sediments are lacking. In this study, coastal surface sediments from 474 geographical locations covering almost the entire island were collected to identify risk-related variables. Controlling factors and possible sources of trace metals were identified, and the toxicity effects were carefully evaluated. Our results suggest that trace-metal pollution in coastal sediments, which was mainly caused by Pb, Zn and Cu emissions, has primarily resulted from industrial sewage and shipping activities and has threatened the offshore ecosystem of Hainan Island and warrants extensive consideration. This is the first study that has systematically investigated trace metal-polluted coastal sediments throughout the entirety of Hainan Island and provides solid evidence for sustainable marine management in the region.

Toxicity and bioaccumulation of copper in Limnodrilus hoffmeisteri under different pH values: Impacts of perfluorooctane sulfonate

Aquatic oligochaete Limnodrilus hoffmeisteri (L. hoffmeisteri) has been commonly used as a lethal and/or sub-lethal toxicological model organism in ecological risk assessments in contaminated water environments. In this study, experiments were conducted to investigate the potential toxic effects of copper (Cu(II)) with or without perfluorooctane sulfonate (PFOS) under different pH values (6.0, 7.0 and 8.0) on LC50, bioaccumulation, and oxidative stress biomarkers in L. hoffmeisteri after 3 and 7 days. The LC50 values of Cu(II) decreased with the increasing pH and the addition of PFOS. After each exposure, increasing bioaccumulation of Cu(II) in L. hoffmeisteri was observed in the combined exposure treatments, whereas the bioaccumulation of PFOS decreased. Moreover, the activity of superoxide dismutase, the level of glutathione, and the content of malondialdehyde were significantly altered after these exposures, possibly indicating that the bioaccumulation of Cu(II) and PFOS caused adverse effects on antioxidant defenses of L. hoffmeisteri. The integrated biomarker response index, indicates that the combined effect was proposed as synergism, which is coincided with the results of toxic unit. Moreover, this work showed that aquatic environment may become more livable when water conditions changed from acidic to near-neutral or alkaline.

Evaluation of single and joint toxicity of perfluorooctane sulfonate and zinc to Limnodrilus hoffmeisteri: Acute toxicity, bioaccumulation and oxidative stress

Perfluorooctane sulfonate (PFOS) and zinc have been detected in aquatic environment widely. In order to study the combined effects of PFOS and Zn, a series of experiments was conducted to explore the acute mortality, bioaccumulation and antioxidant status of Limnodrilus hoffmeisteri. The acute toxicity was evaluated by calculating 24h-EC50 values, and it was observed that 24h-EC50 values in single and joint treatments decreased with decreasing pH value or increasing exposure concentration. Toxic unit analysis suggested that the combined effects of the PFOS+Zn binary mixture were mostly simple addition, with 8 groups showing synergism and only one group showing antagonism. The analysis of internal Zn and PFOS concentration showed that the possible interaction between Zn and PFOS can affect the bioaccumulation of the two chemicals in L. hoffmeisteri. In addition, oxidative stress status was assessed by measuring oxidation-related biochemical parameters such as superoxide dismutase, glutathione peroxidase and malondialdehyde, and the integrated biomarker response index was estimated to rank the toxicity order. Exposures to Zn and PFOS were found to evoke some changes in the antioxidant defense system, and a strong self-adaptive ability was noticed for L. hoffmeisteri after 10 d exposure.

Bioavailability assessment of toxic metals using the technique "acid-volatile sulfide (AVS)-simultaneously extracted metals (SEM)" in marine sediments collected in Todos os Santos Bay, Brazil

This paper reports the bioavailability of the metals (cadmium, copper, zinc, lead, and nickel) in sediment samples collected in seven stations from the São Paulo Estuary, Todos os Santos Bay, Brazil. The bioavailability was determined by employing the technique "acid-volatile sulfide (AVS) and simultaneously extracted metal (SEM)". The elements cadmium, copper, lead, and zinc were determined using differential pulse anodic stripping voltammetry (DPASV), while nickel was quantified utilizing electrothermal atomic absorption spectrometry (ET AAS). The accuracy of these methods was confirmed using a certified reference material of estuarine sediment (NIST 1646). The sulfide was quantified using potentiometry with selective electrode and the organic matter determination employing an indirect volumetric method using potassium dichromate and iron(II) sulfate solutions. The bioavailability of the metals was estimated by relationship between the concentration of AVS and the sum of the concentrations of the simultaneously extracted metals (ΣSEM), considering a significant toxicity when (ΣSEM)/(AVS) is higher than 1. The bioavailability values in the seven stations studied varied from 0.93 to 1.31 (June, 2014) and from 0.34 to 0.58 (September, 2014). These results demonstrated a critical condition of toxicity (bioavailability >1) in six of the seven sediment samples collected during the rainy season (June, 2014). In the other period (September, 2014), the bioavailability was always lower than 1 for all sediment samples collected in the seven stations. The individual values of the concentrations of the five metals were compared with the parameters PEL (probable effects level) and TEL (threshold effects level), which are commonly employed for characterization of ecological risk in environmental systems. This comparison revealed that all metals have concentrations lower than the PEL and only zinc and lead in some stations have contents higher than the TEL. The bioavailability evaluation and the concentrations achieved for the five elements in the sediments samples analyzed demonstrated that the ecosystem studied does not present an environmental risk.