Distribution Patterns Of Arsenic Speciation And Fractionation In Typical Ornithogenic Sediments

It is well known that seabirds act as biovectors between marine and terrestrial ecosystems, and are important material transport pathways in some remote coastal areas. Via this process, considerable toxic contaminants (such as heavy metals) are transported by seabirds to their breeding sites, and may pose potential ecological risks to local ecosystems. Up to now, geochemical research on As (Arsenic) in seabird habitats remains with the general study of total As. In this study, we firstly focused on the distribution patterns of As species and fractionation in the ornithogenic sediments, and also provide important implications for the evaluation of ecological risk caused by penguin-derived heavy metal pollution. These results can help us better understand the environmental geochemistry behavior and potential eco-environmental risk of these heavy metals in Antarctic penguin habitats.1. Quantitative analysis of As speciation in guano and ornithogenic sediments using microwave-assisted extraction followed by HPLC-HG-AFSSeabird guano is one of the main sources of nutrient fertilizers in remote coastal island areas, but guano-derived contaminants such as As may cause serious threats to local ecosystems. In this study, a new method was developed to analyze As speciation in guano and ornithogenic sediments. Good extraction efficiencies of As(Ⅲ) (arsenite), DMA (dimethylarsinate), MMA (monomethylarsonate) and As(V) (arsenate) were obtained by using 1.0 mol L-1 orthophosphoric acid and 0.1 mol L-1 ascorbic acid, followed by microwave-assisted extraction and high performance liquid chromatography coupled to hydride generation atomic fluorescence spectrometry (HPLC-HG-AFS) detection. Under the optimized conditions, the extraction efficiencies of four As species were over 80%. The relative standard deviations (RSD) were 9.60%,6.15%,6.34%,2.93%(n=7), and the detection limits (μg L-1) were 0.82, 2.38,1.45,2.31 for As(lII), DMA, MMA, As(V), respectively. This method was successfully used to determine As speciation in the guano samples collected from the Xisha Islands of the South China Sea, and the results indicated that As(Ⅲ) and As(Ⅴ) were the dominant As species in modern and ancient guano, respectively.2. Distribution patterns and possible influencing factors of As speciation in ornithogenic sediments from the Ross Sea region, East AntarcticaOrnithogenic sediments are rich in toxic As compounds, posing a potential threat to local ecosystems. Here we analyzed the distribution of As speciation in three ornithogenic sediment profiles (MB6, BI and CC) collected from the Ross Sea region. East Antarctica. The distributions of total As and total P (phosphorus) concentrations were highly consistent in all three profiles, indicating that guano input is a major factor controlling total As distribution in the ornithogenic sediments. The As found in MB6 and CC is principally As(Ⅴ), in BI As(Ⅲ) predominates, but the As in fresh guano is largely composed of DMA. The significant difference of As species between fresh guano and ornithogenic sediment samples may be related to diagenetic processes after deposition by seabirds. Based on analysis of the sedimentary environment in the studied sediments, we found that the redox conditions have an obvious influence on the As speciation distribution. Moreover, the distributions of As(Ⅲ) and chlorophyll a in the MB6 and BI profiles are highly consistent, demonstrating that aquatic algae abundance may also influence the distribution patterns of As speciation in the ornithogenic sediments.3. Distribution patterns of As speciation in ornithogenic sediments from Fildes Peninsula of West Antarctica and Xisha Archipelago of South China SeaWe also analyzed the distribution of As speciation in ornithogenic sediment profile (ADY2) and background sediment (LL2) collected from Fildes Peninsula of West Antarctica. The concentrations of total As show good correlations with total P and TOC in ADY2 profile, indicating that guano input is a major factor controlling its total As distribution. The average contents of total P and TOC in ornithogenic sediments are much higher than the background levels, indicating seabird activities have a significant influence on the physicochemical properties of neighboring soils. Inorganic As is the dominant species in these two sediment profiles, and the results of Fe(Ⅱ)/Fe(Ⅱ) indicate redox conditions may explain the difference of As speciation distribution patterns in penguin-affected and background sediment samples. The As in ornithogenic sediments from Xisha Archipelago is largely composed of As(Ⅴ), which is similar to the findings from sediment samples collected in Antarctica.4. Fractionation distribution and preliminary ecological risk assessment of As, Hg and Cd in ornithogenic sediments from the Ross Sea region of East Antarctica and Xisha Archipelago of South China SeaTo evaluate mobility of toxic elements and their potential ecological risk caused by seabird biovectors, the fractionation distributions of As, Hg (mercury) and Cd (cadmium) were investigated in three ornithogenic sediment profiles from the Ross Sea region, East Antarctica. The results show residual As holds a dominant position, and Hg mainly derives from residual, organic matter-bound and humic acid-bound fractions, indicating weak mobility of As and Hg. However, exchangeable Cd occupies a considerable proportion in studied samples, suggesting Cd has strong mobility. The preliminary evaluation of Sediment Quality Guidelines (SGQs) shows adverse biological effects may occur occasionally for As and Cd, and rarely for Hg. Using Risk Assessment Code (RAC), the ecological risk is assessed at moderate, low and very high for As, Hg and Cd pollution, respectively. Organic matter derived from guano is the main factor controlling the mobility of Hg and Cd through adsorption and complexation.The fractionation distribution patterns of As and Hg were determined in ornithogenic sediments collected from the Xisha Archipelago of South China Sea. The results show that residual As is the dominant species, and Hg mainly derives from residual, humic acid-bound and organic matter-bound fractions. The proportions of exchangeable As and Hg in studied sediment samples stay at low levels, indicating weak mobility of these heavy metals (or metalloid). The preliminary evaluation of ecological risk were conducted using SGQs and RAC methods, and the results show that adverse biological effects unlikely occur for As and Hg in studied sediment samples.