Study On Bioavailability, Ecological Risk And Toxicity Of Heavy Metals In Sediment Of Marine Aquaculture Areas

Sediment is the source and sink of pollutants.It is an important part of aquatic ecosystems,it also provide the habitat and food source for many benthic organisms.The heavy metals can be directly or indirectly used by benthic organisms,and do harm to human health through the food chain.As a result,heavy metal pollution and ecological risks in sediments have attracted much attention.Mercury is one of the most toxic heavy metals.Different forms of mercury have large differences in toxicity.Not all mercury can be bioabsorbed.Analysis of mercury morphological and bioavailability can help us understand mercury toxicity in the environment.In this paper,the spiked external mercury input process was used to study the stabilization,morphological transformation and toxic effects of inorganic mercury in marine sediments,and the ecological risks of heavy metals in sediments of marine aquaculture areas was evaluated.The main contents are as follows:?1?A high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry?HPLC-ICP-MS?method was developed for the determination of methylmercury and ethylmercury in marine culture sediments.KBr and CuSO₄ were chosen as the extractant.Separation of analytes was finished in 5 min by using Zorbax Plus C18column,and isobaric elution with a mixture of 60 mmol/L ammonium acetate,0.1%?m/v?L-cystein and 5%?v/v?methanol as mobile phase?1.0 mL/min?.Under the optimized conditions,the linear range was from 0.25 to 10?g/L for methylmercury and ethylmercury with the excellent coefficients better than 0.9998.The detection limits of methylmercury and ethylmercury?as Hg?were 0.3 and 1.2 ng/g,respectively.The hybrid technique was applied to the speciation analysis of mercury in marine culture sediments.Both methylmercury and ethylmercury were not detected in the collected sediment samples.The recoveries of methylmercury and ethylmercury from sediments,at the spiked concentration levels of 5 to 20ng/g,were in the range of 83.6%⁹9%,with the relative standard deviation?RSD?of1.6%⁷.6%.The method could be applied to quantify methylmercury and ethylmercury in marine culture sediment samples with good precisions and accuracies.?2?By adding inorganic mercury to the sediment,the external mercury input was simulated to study its bioavailability and migration in the sediment.The bioavailable mercury in the sediment was determined by single-stage extraction,thin film diffusion,and centrifugation,respectively.0.5 mol/L CH₃COONH₄-0.5 mol/L EDTA?sample liquid ratio1:10,250 rpm for 2 h?,0.03%C₂H₄O₂S-1/15 mol/L Na₂HPO₄?sample ratio 1:10,250 rpm oscillation 2 h?single-stage extraction of extractant,passive collection by film diffusion gradient technique?DGT??placed in sediment with 90%moisture content for 24 h?,simultaneous collection by centrifugation?4000 rpm,centrifugation for 15 min?,Zeeman mercury analyzer was used to determine the content of Hg in the extracts of the three methods?in the collected liquid?,and the correlation between the single-stage extraction and centrifugation methods and the DGT method was analyzed.The bioavailability of Hg in the sediment was evaluated and utilized.The morphological transformation of exogenous Hg in sediments was investigated by HPLC-ICP-MS.The results show that the total amount of mercury in the sediment and the stability time of the external mercury in the sediment can affect its bioavailability.In the case of changes in pollutant concentration,0.5 mol/L CH₃COONH₄-0.5 mol/L EDTA extraction method has a good correlation with DGT determination results?r=0.6877?;In the absence of benthic organism disturbance,the results of 0.03%TGA-1/15 mol/L Na₂HPO₄ extraction method correlated well with DGT results?r=0.6322?.There was a significant positive correlation between the bioavailability of Hg in the sediments measured by single-stage extraction,centrifugation and DGT and the Hg content enriched in the silkworm,of which 0.5 mol/L CH₃COONH₄-0.5 mol/L EDTA extraction method were highly correlated with the amount of Hg enrichment in the silkworm?r=0.9707?.The concentration of bioavailable Hg in the sediments determined by centrifugation and single-stage extraction has a good linear relationship with the amount of Hg enrichment in the silkworm,and the results of centrifugation and the amount of Hg enrichment in the silkworm are one yuan.In the linear equation,k is close to 1,which can be used to estimate the amount of pollutant enrichment in benthic organisms?Silkworm?directly.After the exogenous Hg was stabilized in the sediment?aging for 45 days?,its bioavailability gradually increased,whereas the bioavailability decreased after 14 days of the presence of benthic organisms.Regardless of the presence of benthic organisms,when the exogenous Hg was added to the sediment,the methylmercury content increased with time,and the methylmercury content increased significantly under the benthic perturbation;Morphological transformation of exogenous Hg in the sediment is a combination of biomethylation and chemical methylation.Compared with day 0,methylmercury content in sediments under benthic disturbance is higher?15%¹02%?than that in sediments without benthic organisms,benthic activity is an important factor in biomethylation.?4?By exposing the silkworm to Hg-contaminated sediments,the effects of exposure time and pollutant concentration on Hg enrichment in the silkworm and oxidative stress under Hg stress were investigated.The results showed that mercury was easily enriched in the silkworm,and the enrichment increased sharply with the increase of exposure time and the increase of pollutant concentration.The post-rise rate slowed down and approached the trend of saturation.The malondialdehyde content in the body continued to rise.Trends,the degree of damage to cell membranes in the body is increasing.The molecular level reaction in the silkworm is sensitive to the stress of pollutants.The content of superoxide dismutase,catalase and glutathione in the body increases rapidly to remove active oxygen in the body.?5?The content,bioavailability and fractionation of six heavy metals were investigated in eight maricultural surface sediments from Zhelin Bay.The ecological risk of heavy metals was evaluated by Hakanson index method based on the total metal content and risk assessment code?RAC?based on metal speciation,respectively.The results showed that the concentration of heavy metals in most sites were below the Class?marine sediment quality limit,while the concentration of Zn and Pb in a few sites exceeded the Class?,but not exceeded the Class?.The concentration of bioavailable heavy metals in sediments(C_DGT)measured by the diffusive gradients in thin films technique?DGT?were generally consistent with that in pore water,among which Zn,Ni and Pb were highly bioavailable.Cr,Ni,Zn and Cu in sediments were primarily present in the residual fraction,while Cd and Pb were mainly present in acid-extractable fraction.Conclusively,in Zhelin bay,heavy metals showed slight to moderate ecological risk,among which Cd and Pb showed higher ecological risk compared to other metals.The concentration of bioavailable Cr?Ni?Zn?Cu and Cd(C_DGT)were positively correlated with their acid-extractable fraction in sediments,showing that heavy metals obtained from acid-extractable fraction in sediments can indicate their bioavailability very well.