Accumulation Of Heavy Metals In Multi-phase Media And Their Transfer And Biomagnification In Food Web Of Laizhou Bay

Heavy metal pollution has been one of the major environmental issues inLaizhou Bay in recent years. Such environmental pollution does not only speed up thedecline of many fishery populations, but also affect the structure and functions of theecosystem via the transfer, accumulation and biomagnification of the pollutantsthrough the food chains and webs. Therefore, investigations of the distribution andaccumulation of heavy metals in multi-phase media as well as their toxicologicaleffects on ecosystem are important and necessary for the protection of environment,the rational development and management of living aquatic resources and the safetyof seafood in this region.In the present study, the temporal and spatial distributions and accumulation ofheavy metals (Cr, Cu, Zn, As, Cd, Hg and Pb) in the surface water, sediments andbiotas collected during the seasonal fishery surveys in2010and2011in Laizhou Baywere investigated. Moreover, the transfer, accumulation and biomagnification of thesemetals in the food web as well as their ecological risk were analyzed and assessed.The main conclusions of this research are summarized as follows.(1) Temporal and spatial distribution, source analysis and ecological riskassessment of heavy metals in the surface water and sediments of Laizhou Bay. Thelevels of heavy metals except for Cr and Cu in the surface water showed significantseasonal differences. The water quality indices (WQI) of the seawater were lower than1, indicating that the surface water was generally clean, although slightlycontaminated by Cr and Cu in some sites. Heavy metal levels in the surface sedimentsshowed no significantly seasonal differences but indicated spatial differences. Thehighest levels of Hg and Pb in the sediments were found in Jiehe river estuary and itsadjacent areas, whereas those of Cr, Cu, Zn, As and Cd occurred in Xiaoqinghe riverestuary and the central western areas of Laizhou Bay. Multi-parameters analysis (Enrichment factor, EF; Geoaccumulation index, Igeo; Hakanson potential ecologicalrisk index, RI; Effect range low/median, ERL/ERM) concluded that the surfacesediments were polluted, to varying degrees, by Hg, As, Pb and Cd pollutants.Additionally, principal component analysis (PCA) indicated that Hg and Pb in thesurface sediments were mainly sourced with emissions of anthropogenic pollutants,whereas the other metals were probably affected by natural sources such rockweathering and atmospheric sedimentation. Hierarchical cluster analysis classified thesediments into four categories in terms of the spatial similarity of heavy metalpollution. Category I referred to the Xiaoqinghe river estuary and the central westernareas of Laizhou Bay, being characterized with high levels of Cr, Cu, Zn, As and Cd;Category II comprised the Jiehe river estuary and its adjacent areas, where high levelsof Hg and Pb were found; Category III was mainly distributed in the southern coastalareas of Laizhou Bay. Levels of all heavy metals in these areas were overall at lowlevels; the rest part of Laizhou Bay belonged to Category IV that was characteristic oflow levels of Cr, Cu, Zn and As.(2) Species-and tissue-specific bioaccumulation of heavy metals in fivecommercial fish in Laizhou Bay. Heavy metal concentrations in the tissues (muscle,stomach, liver, gills, skin and gonads) of mullet Liza haematocheilus, flathead fishPlatycephalus indicus, sea bass Lateolabrax japonicus, mackerel Scomberomorusniphonius and silver pomfret Pampus argenteus were studied. The results indicatedthat heavy metal concentrations in the five fish were tissue-specific, with the highestlevels of Cd, As, Zn and Cu in gonads and liver, and the highest levels of Hg ingonads and muscle and those of Pb in gills. Bioconcentration enrichment factor (BCF)of heavy metals in the five fish showed an order of Zn (9.58)>Cr (8.99)>Cd(3.74)>Cu (2.60)>Hg (2.12)>As (1.81)>Pb (0.32). Carnivorous predators (sea bass,flathead fish and mackerel) exhibited higher Hg concentrations in the muscles thanplanktonic and detritivorous consumers (mullet and silver pomfret), whereas Pb andAs exhibited the opposite trend to Hg. Bioaccumulation of other metals in the five fish showed no clear relationship with the feeding habits of fish. Mercurybioaccumulation tended to be positively correlated with fish length and conditionfactor, while Zn and Cu exhibited the opposite trend. Compared with national orinternational permissible limits criteria for heavy metals in fish muscles, it was foundthat As, Cr and Cd in the muscles of the five fish exhibited potential risks for humanconsumption because their concentrations in31%,10%and1.4%, respectively, of themuscles samples exceeded the relevant limits.(3) Bioaccumulation and risk assessment of heavy metals in three bivalves in thecoastal areas of Laizhou Bay. Heavy metal concentrations in the visceral mass andmuscle tissues of three bivalves (art shell Scapharca subcrenata, surf clam Mactraveneriformis and Manila clam Ruditapes philippinarum) collected from the coastalareas were investigated. The results indicated that the bioaccumulation of all theheavy metals except for Cr in the three bivalves were tissue-specific, with higherlevels in visceral mass than in muscle tissues. The highest levels of Cr and Pb werefound in surf clam, while those of Cu, Zn, As and Hg were in Manila clam. Thehighest Cd level was found in art shell. Metal pollution index (MPI) ranged from2.0to3.5for ark shell, from2.4to3.9for surf clam and from3.0to4.9for Manila clam.These results suggested that the highest heavy metal-polluted bivalves weredistributed in Sanshandao area, whereas the least contaminated bivalves were found inXiaying and Yangzi areas. Biota-sediment accumulation factor (BSAF) indicated thatthe bioavailability of heavy metals from sediments followed an order of Cd(58.26)>Hg (3.09)>As (2.18)>Zn (2.05)>Cu (0.47)>Cr (0.03)>Pb (0.02). In addition,the BSAF of Cu, Zn, As, Cd and Pb showed negative correlations with theirconcentrations in the sediments. Bioaccumulations of Cr (R=0.673) and Cu (R=0.573)in surf clam, Zn (R=-0.573) in Manila clam and Cd (R=0.927) in ark shell weresignificantly correlated with their concentrations in the sediments. However, nosignificant cases were found in the biota-sediment accumulation relationship for As,Hg and Pb. Risk assessment of heavy metals in the three bivalves revealed that As and Cd exhibited potential hazards to human consumption because the levels of these twometals in100%and87.5%, respectively, of the muscle samples exceeded their safetylimits.(4) Transfer, accumulation and biomagnification of heavy metals in the foodchains and webs of Laizhou Bay. Heavy metal bioaccumulations in the muscles of46representative species (20invertebrate species and26fish species) in Laizhou Baywere investigated. Stable isotope of nitrogen ratio (δ15N,14N/15N) was applied todetermine the trophic levels of the species. The primary consumer Gastrosaccuspelagicus was used as the baseline species (trophic level, TL=2.0; δ15N=6.720.07‰).The δ15N ratios of all studied species ranged from4.38‰to15.11‰with trophiclevels ranging from1.31to4.47. In terms of taxonomic categories, their TLs showedthe following order: large demersal predatory fish (4.34,4.25-4.47)≈pelagicpredatory fish (4.39)> medium demersal fish (4.01,3.78-4.17)> small demersal fish(3.67,3.36-4.00)≈cephalopods (3.71,3.63-3.78)≈benthonic crustaceans (3.59,3.32-3.99)> gastropods (3.21)> bivalves (1.96,1.31-3.03)≈zooplanktoniccrustaceans (2.28,1.99-2.56)≈polychaetes (1.96). Three types of biomagnificationfactor (BMF; Biomagnification factor of proportion of sources, BMFPSC; Food webmagnification factor, FWMF) were used to assess the biomagnification efficiency ofmetals via food chains or webs. The results indicated that Hg and Cr showed anobvious biomagnification efficiency when they are transferred from primary preysinto the four predatory fish species (sea bass, mackerel, flathead fish, and founderParalichthys olivaceu). The BMFPSCof Cr and Hg for sea bass were2.99and8.24,respectively, remarkably higher than those for mackerel, flathead fish and founder (Cr,1.67–2.42；Hg,1.34–2.96). The positive biomagnification of these two metals wasalso found in the two typical food chains: pelagic grazing food chain and benthicgrazing food chain. BMF of Cr (160.75) in the pelagic grazing food chain wassignificantly greater than that in the benthic grazing food chain (3.11), while the BMFof Hg in benthic grazing food chain (13.57) was higher than that in the pelagic grazing food chain (6.63). In terms of biomagnification on food web, the FWMF ofCr and Hg were3.83and5.26, respectively. Moreover, Cr and Hg demonstrated clearbiomagnification in92.86%of the total14typical trophic interactions (chains)between taxonomic categories (BMF>1). The biomagnification efficiency of thesemetals was estimated be1.72mg/kg dry wt. for Cr and0.09mg/kg dry wt. for Hg.However, the FWMF of other metals ranged from0.17to0.47, suggesting that nobiomagnification efficiency was found in the food webs of Laizhou Bay.