Chemistry Reference
In-Depth Information
CH
3
+
2e
-O
2-
2e
-O
2-
As(V)O
4
3-
Äs(III)O
3
3-
CH
3
As(V)O
3
2-
CH
3
Äs(III)O
2
2-
CH
3
+
CH
3
+
2e
2e
-O
2-
(CH
3
)
2
As(V)O
2
-
(CH
3
)
2
Äs(III)O
-
(CH
3
)
3
As(V)O
(CH
3
)
3
Äs(III)
-O
2-
Trimethylarsine
fIgure 8.6
Methylation of arsenate (after Environmental Health Criteria 18).
of arsenic occurs with the trivalent rather than the pentavalent form, and up to three
methyl groups can be bound to one As atom (Figure 8.6). The final product, trim-
ethylarsine, is both volatile and highly toxic to mammals. It has been implicated in
cases of human poisoning following its generation by microorganisms from inor-
ganic arsenic (Paris Green) in old wallpaper.
Significant quantities of organoarsenic compounds have been found in marine
organisms, and questions have been asked about the possible health risk to humans
consuming sea food.
8.6
Summary
Mercury, tin, lead, arsenic, and antimony form toxic lipophilic organometallic
compounds, which have a potential for bioaccumulation/bioconcentration in food
chains. Apart from anthropogenic organometallic compounds, methyl derivatives
of mercury and arsenic are biosynthesized from inorganic precursors in the natural
environment.
Methyl mercury compounds are neurotoxic and can cause behavioral effects
in vertebrates. They bind strongly to sulfhydryl groups of proteins and can cause
changes in the abundance of neurochemical receptors of the vertebrate brain.
Cases of human poisoning (Minamata Bay incident) and poisoning of wildlife
(Sweden in the 1950s and 1960s) have been caused by methyl mercury. Even after
bans on use of methyl mercury, fungicide levels of methyl mercury are still high
in some areas (e.g., of North America), and there is evidence of continuing side
effects on wildlife.
Tributyltin compounds used as antifouling agents on boats have had serious
toxic effects upon many mollusks, including populations of oysters and dog whelks.
Females of the latter species developed a condition known as imposex, which ren-
dered them infertile and caused local extinction of the population in shallow coastal
waters. Imposex provides the basis for a valuable biomarker assay.
Alkyl lead compounds are also highly neurotoxic and were implicated in large-
scale kills of wading birds.
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