Accumulation of mercury in the terrestrial food chain of the Liaohe estuary wetlands, China.

Mercury is a global pollutant that can be enriched in organisms and eventually endanger human health. In this paper, we studied the soil, plants, and animals in the sandy beach, winged alkali pong wetland, reed wetland, and rice field in Liaohe estuary in 2018 and 2019, measured the plant and animal carbon and stable nitrogen isotopes, and carried out the food chain construction by animal carbon and nitrogen stable isotopes, and studied and analyzed the accumulation of mercury from the producer to the consumer of the food chain. The results showed that the food chain construction at the sampling sites was as follows: S1: plants < flesh worms, ants < spiders; S4: plants < moths, leaf beetles, mosquitoes, ants < spiders; S6: plants < mosquitoes < spiders; S7: plants < flattened hooks, mosquitoes, ants < spiders; S9: plants < ants < spiders. The range of Hg in soil: S1: 0.087-0.175 mg/kg; S2: 0.035-0.197 mg/kg; S3: 0.089-0.249 mg/kg; S4: 0.050-0.167 mg/kg; S5: 0.024-0.150 mg/kg; S6: 0.066-0.152 mg/kg. S7: 0.035-0.165 mg/kg; S8: 0.026-0.083 mg/kg; S9: 0.035-0.191 mg/kg. The range of Hg in plant samples: S1: 0.019-0.242 mg/kg; S2: 0.019-0.161 mg/kg; S3: 0.025-0.142 mg/ kg; S4: 0.010-0.120 mg/kg; S5: 0.015-0.269 mg/kg; S6: 0.040-0.079 mg/kg; S7: 0.014-0.300 mg/kg; S8: 0.020-0.100 mg/kg; S9: 0.022-0.208 mg/kg. Constructing the food chain of In animal samples, the accumulation of Hg: S1: 0.061-0.355 mg/kg; S3: 0.082-0.198 mg/kg; S4: 0.051-0.230 mg/kg; S6: 0.032-0.449 mg/kg; S7: 0.078-0.195 mg/kg; S9: 0.086-0.189 mg/kg By comparing the data, the annual accumulation of heavy metals in soil and plant samples showed an increasing trend and combined with the trophic level relationship of the food chain, it was found that the accumulation trend of heavy metals increased step by step with the trophic level of consumers.

Total and Methylmercury of Suaeda heteroptera Wetland Soil Response to a Salinity Gradient Under Wetting and Drying Conditions.

Mercury (Hg) methylation could occur in freshwater ecosystems with low or high salinity. However, few studies are available about the effects of salinity change on mercury(Hg) release and methylation. In-situ experiments using Suaeda heteroptera wetland soil column from the Liaohe estuary were performed to decipher how total mercury (THg) and methylmercury (MeHg) contents change under fluctuant salinity and wet and dry soil conditions. Salinity gradients were set to 0.50% (S1), 1.00% (S2), 1.50% (S3) and 1.80% (S4), and pure deionized water was used as a blank control (CK). Wet and dry soil conditions were set to full inundation condition (WD1) and naturally dried treatment (WD2). Results indicated that the highest THg and MeHg contents were found in surface and bottom soil when water salinity treatment was CK under WD1. THg and MeHg decreased with salinity under WD1. THg contents in overlying water varied from 0.854 to 1.243 µg L-1 under WD1 treatments and increased with salinity change. When under WD2 treatment, THg contents in both soil layers gradually decreased with rising salinity. Meanwhile, MeHg contents in both soil layers reached the lowest level at CK (1.666 µg kg-1and 2.520 µg kg-1) and increased gradually with the rising salinity. By comparison, THg content of the soil was much lower in WD1 than that in WD2. Under the WD1 condition, the MeHg contents and %MeHg decreased with rising salinity and showed significantly different in different salinity treatment, however, its showed an opposite trend with rising salinity under the WD2 condition.

Salinity and redox conditions affect the methyl mercury formation in sediment of Suaeda heteroptera wetlands of Liaoning province, Northeast China.

Using a laboratory simulation experiment, we studied the trend of change in methylmercury (MeHg) content of sediments in response to the changing salinity of flooding water (deionized water, 0.5%, 1.0%, 1.5%, and 2.0%) and sulfate-reducing bacteria (SRB) content for both the surface layer (0-10 cm) and the bottom layer (10-20 cm) of Suaeda heteroptera wetland sediments in the Liaohe estuary under anaerobic and aerobic conditions, respectively. The results showed that under AAC (anaerobic conditions), the MeHg content in the surface and bottom sediment layers increased first and then decreased over time and was highest at the 14th day. In contrast, under AC (aerobic conditions), the MeHg content in sediments of both layers increased slowly with increasing test time. The MeHg content in sediments increased first and then decreased with rising salinity and was highest at a salinity of 1.0%. Among the samples collected at different experimental stages, the SRB content in the sediments showed a decreasing trend with rising flooding salinity under AAC and AC. The MeHg and SRB contents were higher under anaerobic conditions than under aerobic conditions. Linear fitting results showed that there was no linear correlation between MeHg contents and SRB quantities in surface and bottom sediments under AAC and AC (R2 < 0.1). Collectively, these results suggest an important role for flooding salinity and anaerobic-aerobic conditions in the production of MeHg in S. heteroptera wetlands of the Liaohe estuary, and may predict the ecological risk of methylmercury according to the change of salinity.