Abstract
Arsenic species including arsenite As(III), arsenate As(V), monomethylarsenate (MMA), dimethylarsenate (DMA), and some diagenetic constituents (Fe, Mn, and S2−) in porewaters along with the unstable arsenic species in sediments collected from a typical intertidal zone of Bohai Bay in China were measured. Their vertical distributions were subsequently obtained to reveal the transportation and transformation characteristics of arsenic at the intertidal sediment-water interface (SWI). Results show that the reduction of As(V) by microorganisms occurred in sediments, but the methylation of arsenic by microorganisms was weak in the intertidal zone. The distribution of As(V) was mainly controlled by Mn, whereas As(III) appeared to be more likely controlled by Fe. Arsenic in sediments mainly existed in a stable state, so that only little arsenic could be released from sediments when the environmental conditions at the SWI are changed. As(III) diffused from porewaters to the overlying water while the opposite was true for As(V) at that time when the samples were collected. The total diffusion direction for arsenic across the SWI was from porewaters to the overlying water with a total diffusive flux estimated at 1.23 mg·m−2·a−1.
Highlights
Our knowledge about the arsenic (As) cycles and species in marine sediments, especially in intertidal sediments, is limited. e ubiquitous use of anthropogenic arsenic associated with rapid economic development has significantly changed their original distribution patterns in natural environments, enabling their delivery to the intertidal zone from river catchments via fluvial transport, atmospheric deposition, and local wastewater discharge. e most common species of arsenic likely to be found in aquatic environments are arsenite As(III) and arsenate As(V) [1], but methylation probably occurs by activity of microorganisms, resulting in the formation of organic arsenic compounds such as monomethylarsenate (MMA) and dimethylarsenate (DMA) [2, 3]. e strong toxicity of inorganic arsenic leads to the important significance to carry out geochemical studies of arsenic in the environment
We found that total organic matter (TOM) in this investigated site was especially high with an average content of 10.62% (Figure 2(a))
TFe in sediments was quite high with an average value of 29.36 g·kg−1, while the labile EFe only accounted for about 23.13% (Figure 2(c)), indicating iron in intertidal sediments mainly existed in stable sulfides or in a residual state
Summary
Our knowledge about the arsenic (As) cycles and species in marine sediments, especially in intertidal sediments, is limited. e ubiquitous use of anthropogenic arsenic associated with rapid economic development has significantly changed their original distribution patterns in natural environments, enabling their delivery to the intertidal zone from river catchments via fluvial transport, atmospheric deposition, and local wastewater discharge. e most common species of arsenic likely to be found in aquatic environments are arsenite As(III) and arsenate As(V) [1], but methylation probably occurs by activity of microorganisms, resulting in the formation of organic arsenic compounds such as monomethylarsenate (MMA) and dimethylarsenate (DMA) [2, 3]. e strong toxicity of inorganic arsenic leads to the important significance to carry out geochemical studies of arsenic in the environment.Bohai Bay is a semienclosed shallow water basin located in the western region of the Bohai Sea in the northern China. Our knowledge about the arsenic (As) cycles and species in marine sediments, especially in intertidal sediments, is limited. E most common species of arsenic likely to be found in aquatic environments are arsenite As(III) and arsenate As(V) [1], but methylation probably occurs by activity of microorganisms, resulting in the formation of organic arsenic compounds such as monomethylarsenate (MMA) and dimethylarsenate (DMA) [2, 3]. Due to the large amount of contaminant inputs and poor physical self-cleaning capacity, Bohai Bay has become one of the most degraded marine systems in China. E toxicity and mobility of arsenic in aquatic environment largely depend on its chemical form [6, 7]. Inorganic As(III) is generally more toxic than As(V), while organic arsenic compounds are generally
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