Wednesday, 31 December 2014

The effect of non-lethal Carbosulfan exposure on Rainbow Trout.

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.

 A commercially availble brand of Carbosulfan. Juanco SPS Ltd.

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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