Carbosulfan, 2,3-dihydro-2,2-dimethyl-7-benzofuranyl
(di-n-butylaminosulfenyl) methyl carbamate, is a carbamate pesticide which was
banned in for use the European Union in 2007, but is still manufactured for
export, and is widely used in countries such as Mexico, Brazil, India and Sri
Lanka. It is used on a wide variety of crops, particularly Citrus fruits, Corn,
Soya beans and Rice. Carbamate pesticides, like organophosphates, act by
inhibiting the enzyme acetylcholinesterase by reacting with its active sites,
i.e. they are neurotoxins which halt synaptic transmission in the nervous
system. Such toxins readily enter the aquatic ecosystem, where they are harmful
to Fish and aquatic invertebrates, but break down rapidly in the environment,
which can make them hard to detect by analysis of water samples.
In a paper published in the Turkish Journal of Fisheries and AquaticSciences on 24 September 2014, Erol Capkin of the Department of Marine Sciences andTechnology Engineering at Karadeniz Technical University, Halis Boran of the Department
of Fisheries and Aquatic Sciences at Recep Tayyip Erdoğan University and Ilhan Altinok,
also of the Department of Marine Sciences and Technology Engineering at
Karadeniz Technical University, discuss the results of an experiment in which
Rainbow Trout, Oncorhynchus mykiss,
were exposed to sub-lethal levels of Carbosulfan exposure over a period of 60
days, with enzyme activity in the blood and liver monitored during this period
and a 24 day recovery period.
The exposure of the Fish to the toxin was gauged at levels known to
be sublethal, and none of the Fish died during the procedure. Fish exposed to
Carbosulfan showed a number of abnormalities compared to Fish in a control
group, including loss of balance, darkening in colour and reduced feeding.
There was some improvement during the second week of exposure, suggesting that
the Fish were able to adapt to Carbosulfan exposure to some extent. The exposed
showed a much reduced growth rate compared to the control group, gaining only
3% bodyweight over the course of the experiment, compared to 39% in the
unexposed Fish.
The exposed Fish showed reduced protein levels in the liver, a
symptom of metabolic degradation (the liver is the principle organ used for the
removal of toxins from the body by vertebrates). They also showed reduced
levels of acetylcholinesterase activity in the blood and liver, with the liver
affected more than the blood. The level of enzyme activity in the blood had
returned to normal 18 days after exposure ceased, while that in the liver
recovered after 21 days.
A Rainbow Trout, Oncorhynchus mykiss. Wikimedia Commons.
From this Capkinet al. conclude
that freshwater Fish are useful biomarkers for the presence of the toxin in
aquatic ecosystems, even if it is not present at levels high enough to be
lethal. They suggest that it should be possible to monitor for the presence of
Carbosulfan by taking blood samples from wild Fish, a relatively simple procedure
which can be carried out in the field.
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