Temporal and spatial variation in Hg accumulation in zebra mussels (Dreissena polymorpha): possible influences of DOC and diet

Trends and Causes of Raw Water Quality Indicators in the Five Most Famous Lakes of Jiangsu Province, China

Due to pollutants from industrial and agricultural activities, the lakes in China are faced with ecological and environmental problems. The five most famous lakes of Jiangsu Province, Taihu Lake, Gehu Lake, Gaobaoshaobo Lake, Hongze Lake, and Luoma Lake, have long-term fixed monitoring points for water body-related indicators. Over a five-year period, the monitoring showed that Gehu Lake had the highest average total nitrogen (TN) and total phosphorus (TP) concentrations among all lakes which were close to the Grade V critical value of the China’s Environmental Quality Standards for Surface Water (CEQSW). The NH₃-N concentrations in all lakes were Grade IV according to the China’s Water Quality Standard for Drinking Water Sources (CWQSDWS) and Grade II according to the CEQSW. In addition, although TP concentrations in Taihu Lake did not exceed Grade V in the CEQSW, TP removal was the main factor controlling eutrophication. It was also found that the petroleum concentrations in all lakes were lower than the Grade I according to the CEQSW. Despite this relatively low petroleum pollution, the concentration of petroleum was negatively correlated with the phytoplankton densities in all lakes. This indicated that phytoplankton density was very sensitive to petroleum concentration. For heavy metals, the concentrations of Pb, Cu, As, and Cd in all lakes were significantly lower than Grade I (CEQSW) from 2013 to 2017. However, the accumulated heavy metals in sediments will remain an important pollution source affecting water quality and aquatic products in the future. The comprehensive pollution index analysis showed that the five lakes were often moderately polluted, indicating that the protection of lake resources in China should not be relaxed for a long time in the future.

Genotoxic potency of mercuric chloride in gill cells of marine gastropod Planaxis sulcatus using comet assay

In vivo and in vitro exposures were used to investigate the genotoxicity of mercuric chloride (HgCl2) to the marine snail, Planaxis sulcatus. The comet assay protocol was validated on gill cells exposed in vitro to hydrogen peroxide (H2O2, 0-50 μM). Snails were exposed in vivo for 96 h to HgCl2 (10, 20, 50, and 100 μg/l). Our results showed significant concentration-dependent increase in the tail DNA (TDNA) and olive tail moment (OTM) in exposed snails for all doses compared with controls. In vitro exposure to HgCl2 (10-100 μg/l) resulted in significantly higher values for TDNA at all concentrations. Our results showed that DNA damage increased in the gill cell with increasing exposure time. This study demonstrates the usefulness of comet assay for detection of DNA damage after exposure to HgCl2 and the sensitivity of marine snail P. sulcatus as a good candidate species for metal pollution.

Separating natural from anthropogenic causes of impairment in Zebra mussel (Dreissena polymorpha) populations living across a pollution gradient

The relationship between the reproductive stage, the total lipid content and eight broadly used biochemical stress responses were used to assess seasonal and pollutant effects across eleven different zebra mussel (Dreissena polymorpha) populations from the Ebro and Mijares river basin, Spain. Biochemical markers included superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), glutathione S transferase (GST), multixenobiotic transporter activity (MXR), lactate dehydrogenase (LDH), lipid peroxidation (LPO) and single strand DNA breaks. Principal component analyses of zebra mussel responses across an annual cycle, showed a marked gonad stage component in total lipid content and biochemical responses. The same response pattern was observed across the populations sampled along a broad geographical and pollution gradient. Population differences on the gonad developmental stage were highly correlated with most of the measured responses and unrelated with the pollution gradient. Conversely, bioaccumulation of organic and inorganic contaminant residues was more related to pollution sources than with the reproductive cycle. These results indicate that the reproductive cycle is the major factor affecting the temporal and spatial variation of the studied markers in D. polymorpha.