Pollution Characteristics And Ecological Risks Of Arsenic In The Water Environment Of Laizhou Bay And Its Estuarie

Laizhou Bay is located in the south of the Bohai Sea,which is knows as the three major bays of Bohai Sea together with Liaodong Bay and Bohai Bay,and is a typical semi-enclosed bay.In recent decades,with the rapid social and economic development along the coast of Laizhou Bay,the environmental pollution in Laizhou Bay has become increasingly serious.Multiple inflow rivers,such as the Yellow River and the Xiaoqing River,are the main sources of environmental pollution in Laizhou Bay,while the estuary is a transition zone connecting the inflow rivers with the sea.Part of the pollutants discharged into river enter the ocean with the river,and the other part migrates and transforms in the river water,eventually settles into the sediment.As a metalloid,arsenic（As）has strong toxicity and potential threat to the survival and development of human beings and organisms.It is important to systematically study the As pollution status in the water environment of Laizhou Bay,explore its influencing factors of As pollution,clarify the ecological risks of As,formulate environmental protection measures for this sea area,and maintain the health and sustainable development of the ecosystem.Based on a systematic study of the content and temporal and spatial distribution characteristics of As in water,suspended particulate matter,and sediment in the Laizhou Bay and its inflow river estuaries,this study systematically evaluates its potential ecological risks The research results provide important basic data and scientific basis for environmental governance,risk prevention and control in Laizhou Bay.The main research conclusions were as follows:（1）Content characteristics of As:The dissolved As in the inflow estuaries and the bay waters during the dry season ranged from 1.76 to 5.72（mean:4.51）μg·L^-1 and 0.82 to 3.54（mean:1.98）μg·L^-1,respectively.During the normal season,the contents ranged from 0.54 to 2.11（mean:1.51）μg·L^-1 and 0.34 to 1.32（mean:0.75）μg·L^-1,respectively.During the wet season,the contents ranges from 0.26 to 2.78（mean:0.52）μg·L^-1 and 0.12 to 0.52（mean:0.28）μg·L^-1,respectively.The suspended particulate As（normal season）ranged from 0.04 to 1.34（mean:0.68）μg·L^-1 and0.02 to 0.47（mean:0.12）μg·L^-1,respectively.The sedimentary As（normal season）ranged from8.93 to 22.46（mean:17.05）mg·kg^-1 and 3.61 to 19.32（mean:12.22）mg·kg^-1,respectively.The results of this study showed that the dissolved As content in the three different hydrological periods was lower than the Class I value in the“Seawater Quality Standard”;The monitoring values of As in sediment at 83.3%were higher than the background values of As in sediment,but the monitored values of sedimentary As at the sampling sites were all lower than the national Class II standard values for marine sediment.（2）Spatial and temporal distribution characteristics of As:The dissolved As content in the study was highest during the dry season,followed by the normal season and lowest during the wet season.indicating that precipitation and dilution of rivers had an important effect on the dissolved As distribution.The content of As in the inflow estuary was higher than that in the bay,and the distribution regularities in the bay was gradually decreasing from the coast to the inner bay.The results indicated that the input from the river was the main source of As pollution in Laizhou Bay.In addition,except pollution sources,the internal circulation in the bay also had important impact on the distribution of As in the bay.（3）Fractionated content characteristics of As:Sedimentary arsenic was fractionated by selective sequential extraction.The As content of each fractionated was in following order:amorphous and poorly crystalline Fe and Al hydrous oxides bound As（F3）>specifically sorbed As（F2）>residual As（F5）>and well-formed crystalline Fe and Al hydrous oxides bound As（F4）>non-specifically sorbed As（F1）.The content of different five As fractionated increased with the increased of total As content,the distribution regularities in Laizhou Bay and its inflow estuary was highly similar to that of sedimentary As.In addition,the highest levels of biological availability As were found in the Xiaoqing River estuary and nearby offshore areas,and the highest levels of Fe-Al-oxide bound As（F3+F4）were found in the Yellow River estuary and nearby offshore areas.（4）Relationship between As and environmental factors:Dissolved As was positively correlated with dissolved organic matter（DOM）,iron（Fe）and aluminum（Al）contents in all samples from the inflow estuary and bay for all three hydrological periods.Dissolved As was a positively correlated with salinity in the estuaries.while dissolved As was a negatively correlated with salinity in the bay waters during the dry season and normal season.Meanwhile,the suspended particulate As was significantly positively correlated with salinity in the inflow estuary（P<0.05）,and significantly negatively correlated in the bay（P<0.05）.It was shown that salinity had an important influence on the environmental behavior of As in inflow estuaries and bay.The contents of clay,TOC,Fe and Manganese（Mn）were positively significantly correlated with As（P<0.05）,and As and phosphorus（P）content of the water and sediment showed a highly significant positive correlation（P<0.01）.The physicochemical properties of the sediment had an important influence on the geochemical behavior of As.（5）The pollution levels and ecological risk of As:The single factor pollution index indicated that dissolved As was at zero pollution level in the study area for all three hydrological periods.The single factor pollution index,idex of geoaccumulation,sediment quality guidelines,enrichment factor index and potential ecological risk index indicated that the pollution level of sedimentary As in the inflow estuary was higher than that in the bay,but the overall level is non-pollution and slight pollution.The comparison between the secondary phase and the primary phase indicated that the content of secondary phase As in the sediment in the study area was relatively high.However,due to the low total content of sedimentary As,the secondary phase As will not cause great pollution to the study area.Therefore,the As pollution level of Laizhou Bay and its inlet estuary was low on the whole,but the pollution evaluation based on morphology showed that the potential ecological risk of the study area may be slightly higher than that of other areas under the same As pollution level.