Bioaccumulation And Transformation Of Inorganic Arsenic In Laminaria Japonica And Toxicological Effect

Arsenic is a kind of metalloid which exists naturally in the marine environment and is one of the known carcinogens in human beings.Due to the bioaccumulation effect of macroalgae and its numerous benefits as food,arsenic accumulated in algae can easily be transferred to humans through the food chain,with complicated effects on human health.Different species of arsenic have different toxicity,of which trivalent arsenic are the most toxic species,followed by pentavalent arsenic and organic arsenic.Arsenosugars and arsenolipida are usually considered nontoxic.At present,the related researches on Laminaria japonica are mainly focusing on the extraction,separation and functional of bioactive substances and the exploration of L.japonica culture mode,while the physiological effects of environmental factors,especially heavy metal stress on L.japonica and its enrichment are not clearly understood.Therefore,the study on the bioaccumulation,transformation and toxicity of arsenic in L.japonica sporophyte can provide a basis for the risk assessment of seafood consumption.It also can provide a certain data reference for the application of marine algae in arsenic detoxification.In this study,arsenite and arsenate were added to culture sporophyte seedlings of L.japonica,and the species and contents of arsenic in culture water and were detected at a certain time to study the uptake and transformation effect of arsenic in L.japonica;The growth,chlorophyll fluorescence parameters,oxidative-antioxidative index and DNA methylation of L.japonica were tested in order to obtain the toxic effect of inorganic arsenic on L.japonica at the experimental concentration.1)Speciation of arsenic in seawater after mariculture.Four concentrations?0.2,0.4,0.8 and 1.6?mol/L?of arsenite?As?III??and arsenate?As?V??were added to L.japonica culture for a period of 28 days.The arsenic species in the water were analyzed at 0,1,2,3,4,7,14 and 28 days,respectively.It was found that As?III?and As?V?could be detected in the water of both arsenic treatments.As?V?was detected in the water of each As?III?exposed group on the first day,and the concentration increased with the exposure time.Only As?V?was detected in the water of the two high concentration groups on the 14th day.As?III?was not detected in all exposed groups.While under As?V?exposure,with the increase of exposure concentration,the earlier As?III?appeared,and the higher the concentration became as well,but only As?V?was detected in all the exposed groups at 14 and 28 days.The change of arsenic species in exposed groups indicated that L.japonica could have a certain effect on arsenic species in seawater,especially on As?III?in the environment.2)The bioaccumulation and transformation of arsenic in L.japonica exposed to inorganic arsenic.The results showed that the total arsenic content of L.japonica was higher in the high concentration arsenic exposed groups,and the total arsenic content under As?III?exposure increased with time,reached the maximum value at the 28th day;While the total arsenic content in L.japonica under As?V?exposure increased first and then decreased,and they were significantly higher than the initial value?P<0.05?.At the end of the experiment,the total arsenic content in the As?V?exposed group was significantly lower than that in As?III?respectively,which indicated that the ability of L.japonica sporophyte seedlings to accumulate arsenite was greater than that of arsenate.It was found that organic arsenic was the main species of arsenic in L.japonica,and the C_{?In As?}/C_?As?in As?III?exposed group was larger than that in As?V?exposed group.On the 7th day and 14th day,As?III?and As?V?were found in all arsenic exposed groups.With the increase of exposure concentration,DMA and MMA were also detected in the As?III?exposed group,but the content of MMA was less?0.048-0.077 mg/kg?,and MMA was not detected in the As?V?exposed group.As?V?dominated the inorganic arsenic species in all arsenic exposed groups during the experiment,and only As?V?was detected in the 0.2 and 0.4?mol/L As?III?exposed groups and 0.2?mol/L As?V?exposed group at 28 d of the experiment.It was suggested that L.japonica may transform the accumulated inorganic arsenic into As?V?and organic arsenic to resist arsenic stress.3)The effects of inorganic arsenic on the growth and photosynthetic fluorescence parameters of L.japonica.Within the range of arsenic concentrations,the weight of L.japonica in all experimental groups increased significantly at 7 d,and the growth rate of L.japonica in As?III?exposed groups decreased with the increase of concentration,only 0.2?mol/L exposed group had no significant difference with the control group.The daily growth rate of As?V?treatment groups were significantly lower than that of the control group.The sporophyte of L.japonica kept growing until the 28th day,and no evidence of arsenic poisoning was observed.The results of chlorophyll fluorescence parameters showed that in addition to the lowest concentration As?III?increasing the Fv/Fm,other concentrations of exposure had no significant effect on Fv/Fm and Yield of sporophyte seedlings.As?V?exposure could promote chlorophyll fluorescence parameters,the high concentration of As?V?significantly increased the Yield.The results showed that the L.japonica was still in a healthy state and maintains growth in the concentration range,but the high concentration exposure of inorganic arsenic would slow down the growth rate of L.japonica,on which As?III?exposure had a greater impact,As?V?promotes the photosynthetic efficiency of L.japonica to some extent.4)Effects on the antioxidant defense system and DNA methylation of L.japonica exposed to arsenic.Malondialdehyde?MDA?and hydrogen peroxide?H₂O₂?levels were significantly higher in the As?III?and As?V?treatment groups than those in the control group.Superoxide dismutase?SOD?and catalase?CAT?activities in L.japonica increased first and then decreased during 7 days.At 28 d,the activity of antioxidant enzymes was still at a high level.At the end of the experiment,the DNA methylation level of the L.japonica sporophyte seedlings in the exposed group showed a increase to different degrees,on which As?III?exposure and low concentration As?V?exposure had little effect.The DNA methylation level of V-b,V-c and V-d groups at 28 d was significantly higher than that at 1 d?P<0.05?.The results showed that arsenic stress caused certain oxidative damage to L.japonica,which could be slowed down by activating antioxidant enzyme system in the short term,but the long-term arsenic exposure would reduce the antioxidant capacity of L.japonica.The L.japonica could deal with arsenic stress by promoting the methylation modification of some special genes in the genome DNA.