| Seaweed is an important biological taxa in marine ecosystems.It can absorb the substances of eutrophication,such as N,P,and release oxygen,which can effectively improve ecological environmental quality in mariculture zones.It is an important ecological and environmental material in coastal water.Seaweed has features of fast growth,extensive cultivation,low cost,strong ability to adapt to the environment,and it can be consumed by humans and aquatic animals,such as abalone and rabbitfish.The purpose of this study was to evaluate both the bioremediation of heavy metals in seawater and sediments by the cultivated seaweed Gracilaria lemaneiformis in Nan'ao Island,China.Further,the study will also evaluate the antagonism of selenium?Se?-enriched G.lemaneiformis to Cd.Samples were collected from December 2014 to July 2015,January to June 2016,and January to April 2018 from 8 zones,including:G.lemaneiformis culture?G?;fish culture?F?;control?C?;shellfish culture?S?;G.lemaneiformis and shellfish mixed culture?GS?;abalone culture?A?;abalone and seaweed mixed culture?GA?;and transition?T?zones.The protection of Se-enriched G.lemaneiformis against Cd toxicity in abalone?Haliotis discus hannai?and rabbitfish?Siganus oramin?were assessed using indices,such as heavy metal concentrations?Se,Cd,Pb,Cu,Zn,Cr?,growth rate,glutathione peroxidase,catalase,superoxide dismutase enzymatic antioxidants activity,malondialdehyde,and metallothionein concentration.Major results are:?1?Heavy metal concentrations in some zones of the Shenao Bay exceeded the standard of water quality,with Cr and Zn exceeding the standard seriously.Most surface waters of Shenao Bay were mildly or moderately polluted by heavy metals.In the surface sediments,the heavy metals,Cd,Pb,Cu and Zn,were enriched to a certain extent.Finally,these metals mainly came from terrestrial inputs of human activities.?2?G.lemaneiformis had a strong ability to accumulate heavy metals,and had a bioremediation effect on water pollution caused by the heavy metals Zn,Pb,Cd and Cu.The heavy metal adsorption capacity of G.lemaneiformis varied during different growth periods and and increased with the growth of G.lemaneiformis.The heavy metal Bioconcentration Factors?BCF?with values of 4.31×103for Cu,1.95×103for Zn,1.90×103for Pb and 1.44×104for Cd.The concentrations of Cd(0.82-2.63?g g-1)and Pb(2.99-3.21?g g-1)in G.lemaneiformis exceeded the limits for contaminants in food?seaweed?,therefore,the safety of G.lemaneiformis should be a concern.?3?The enrichment capacity of Cu,Zn,Pb and Cd in different tissues of abalone and rabbitfish varied.Cu and Zn had strong enrichment in the skin,gills and liver of rabbitfish;Cd and Pb had strong enrichment in the liver and gills of rabbitfish.Pb had strong enrichment in abalone.This indicated that the enrichment of heavy metals in the non-digestive organs of the rabbitfish and abalone mainly came from the adsorption of seawater,rather than through the food chain.The concentrations of Cu,Pb,Cd and Zn in the muscle of small rabbitfish and abalone was lower;therefore,it is deemed safer to eat small rabbitfish and abalone products.In the cultivation system of G.lemaneiformis,heavy metals can be transferred through complex processes such as adsorption,absorption,ingestion,accumulation and excretion,which constitute their migration and transformation in the food chain.?4?The concentrations of Cd,Pb,Cu,and Zn in the sediments were significantly different among the different types of mariculture areas.The concentrations varied widely:Cd?0.04-1.02??g g-1;Cu?1.19-37.70??g g-1;Pb?8.45-74.45??g g-1;and Zn?36.80-201.24??g g-1.G.lemaneiformis can decrease the comprehensive heavy metal pollution and purify the water quality in coastal mariculture zones.The concentrations of these metals in sediments are significantly different among the different types of mariculture areas.G.lemaneiformis enriches the concentrations of these metals in the water,and decreases their surface sediments,resulting in lower concentrations than the sediment quality guidelines?SQG?values and the geoaccumulation index(Igeo),in most stations.The pollution load index?PLI?indicated that heavy metal pollution was lowest in the cultivation zones.The hierarchical cluster and principle component analysis indicates that most of the elements contributed high negative loadings to factor 1.G.lemaneiformis cultivation zone was grouped together near the left side of the x-axis,far away from the heavy metals,indicating that the heavy metal concentrations in G.lemaneiformis cultivation zones was low.The other groups,transition zone,control zone,fish culture zone and shellfish culture zone,were scattered.G.lemaneiformis cultivation may influence and decrease the heavy metal concentrations of sediments in open sea mariculture zones,as well as in coastal marine sediments.?5?Three days of exposure to Se resulted in a significant increase in the metal concentrations in G.lemaneiformis,with a total Se of 49?g g-1,of which 80.5%is organic and 19.5%inorganic.There was no significant increase in metal concentration in abalones in the control treatment throughout the 28-day period.The Se concentrations in abalones increased significantly from the Se-Gracilaria treatment after 1 day of exposure.Se concentrations in abalones did not increase significantly within the first day with Gracilaria treatment,but continued to increase during the remaining exposure period.There was a significant correlation between the metallothionein concentration,glutathione peroxidase activity and the concentration of Se?positive?and Cd?negative?in abalones.The present study demonstrated that dietary Se protects abalone against Cd toxicity,and promoted growth of abalones significantly.Dietary Se was found to alleviate Cd-induced toxicity by enhanced metallothionein generation and the activity of glutathione peroxidase enzymatic antioxidants.The possible antagonistic effects of dietary Se on waterborne Cd-induced toxicity occurs via both enzymatic and non-enzymatic antioxidative mechanisms.?6?The total Se concentration?organic Se and inorganic Se?for the 250 mg L-1Se treated G.lemaneiformis was significantly higher than that of the 50 and 10 mg L-1treatments after Se enrichment for 3 days.The mean total Se concentrations in G.lemaneiformis treatments were 42.5?g g-1in the 250 mg L-1treatment,13.5?g g-1in the50 mg L-1treatment,and 2.5?g g-1in the 10 mg L-1treatment.Organic Se accounts for80-82%of total Se.Dietary Se-enriched G.lemaneiformis can significantly increase the Se concentrations in rabbitfish.Further,it can increase the Cu and Zn absorption,enhance metallothionein generation,improve the activity of glutathione peroxidase,catalase,and superoxidase dismutase enzymatic antioxidants,and decrease the malondialdehyde concentrations and lipid peroxidation levels,which were antagonistic with Cd,Pb and Cr.The antagonistic effects of Se-enriched G.lemaneiformis on waterborne Cd,Pb and Cr-induced toxicity occurs via both enzymatic and non-enzymatic antioxidative mechanisms.Se has synergistic effects with Zn and Cu in rabbitfish.For the 50 mg L-1Se treatment the Se,Cu and Zn,and antagonistic Cd,Pb,Cr are slightly higher than for the 250 mg L-1and 10 mg L-1treatments.For the 50 mg L-1Se treatment the antioxidant enzymes catalase,superoxidase dismutase and glutathione peroxidase activities and metallothionein concentrations were higher than for the 250 mg L-1and 10 mg L-1treatments.Therefore,the 50 mg L-1Se treatment of G.lemaneiformis was the optimum concentration to promote growth in rabbitfish. |
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