The Influence Of Aquaculture On Mercury Speciation Change In The Sediment

Fish aquaculture activities may result in an abnormal accumulation of both organic waste and antibiotics in the underneath sediment,where the methylation of mercury?Hg?mostly occurs.The input of organic waste and antibiotics may influence the methylation of Hg in the sediment underneath the aquaculture rafts.In this study,field investigations and simulation experiment were conducted with attempts to reveal the roles of marine fish aquaculture in distribution of Hg and antibiotics in sediment as well as in Hg methylation by the continuous input of organic waste and antibiotics.The major findings are summarized as follows:1.The results of field investigation showed that total mercury?THg?,methylmercury?MeHg?and percentage of MeHg to THg?%MeHg?in the aquaculture sediments were much higher than those in the reference sites,indicating fish aquaculture activities indeed resulted in the accumulation of THg and promoted Hg methylation.THg content in summer was significantly higher?P<0.05?than that in winter by an increase of 11.9%in the sediments at mariculture sites.However,THg contents in summer was significantly lower than that in the winter?P<0.05?.MeHg content in sediments decreased gradually from surface to bottom layer,which means MeHg are easier to be formed at the interface between water and sediment sites;among the five kinds of antibiotics,oxytetracycline and tetracycline were the highest in the sediments of Zhoushan island with an average concentration of 18.65ng·g^-1 and8.66 ng·g^-11 at aquaculture sites respectively while only 2.01 ng·g^-1 and 0.96 ng·g^-1 were detected at reference sites,respectively.2.The simulation experiment indicated that MeHg concentration and%MeHg in the maricutlrue sediment which was rich in organic waste were significantly higher than those in reference sediment after the addition of inorganic Hg²⁺,although THg remained almost same throughout the whole experiment.It implies that the richness of organic waste in mariculture sediment was beneficial for the methylation of Hg in comparison with the reference sediment.It was noted that the MeHg content in the sediments and%MeHg decreased gradually during the culture experiment period.MeHg concentration in sediment were positively correlated to the addition dosage of Hg²⁺;meanwhile,the%MeHg in the sediments somehow gradually decreased,which may be attributed to the fact that the promotion effect of organic waste on the methylation of Hg existed a threshold due to the limit availability of-CH₃donors.3.The results showed that THg and antibotics concentration in sediment decreased after 64 days of culture period,which indicated that the addition of Hg²⁺in the sediments was complexed with the antibiotics,resulted in the transport of electron from antibiotics to Hg²⁺and thereafter reduction of Hg^2+.to Hg⁰,which could be emitted to the atmosphere.Meanwhile,it was noted MeHg concentration and%MeHg in the treatments with antibiotics addition was substantially increased in comparison to control,especially those with low dosage addition of Hg²⁺.These results illustrated that the presence of antibiotics could promote MeHg formation in sediment.