Toxicity of a mixture of 2,4-dichlorophenoxyacetic acid and monosoduim methanearsonate to the red swamp crawfish, Procambarus clarkii.

2,4-dichlorophenoxyacetic acid and monosodium methanearsonate are often sold in commercial herbicide mixtures. Toxicity studies have been performed for each herbicide individually, but there is a dearth of information concerning the toxicity of these herbicides in a mixture. The following study examined the toxicity of a mixture of these two herbicides in the red swamp crawfish, Procambarus clarkii. 96-hour acute toxicity assays were performed to determine whether surfactant significantly altered the toxicity of these herbicides individually or in combination. Markings additive index was calculated to identify the interactions of the herbicide mixture. Surfactant was observed to significantly increase the toxicity of 2,4-dichlorophenoxyacetic acid and the toxicity of the herbicide mixture. The herbicide mixture alone displayed half the toxicity of the individual herbicides, but the mixture with surfactant was twice as toxic as the individual herbicides. The synergistic action of surfactant may be attributed to increased pesticide absorption across biological membranes. 2,4-dichlorophenoxyacetic acid and surfactant may also compromise gill function, increasing the sensitivity of the crawfish to herbicide toxicity. The antagonistic effects of the herbicide mixture in the absence of surfactant may be caused by competition of both herbicides for the same sites of activity.

Effects of long-term exposure of the red swamp crawfish Procambarus clarkii to a mixture of two herbicides, 2,4-dichlorophenoxyacetic acid and monosodium methanearsonate, and associated human health risks.

2,4-dichlorophenoxyacetic acid and monosodium methanearsonate are often sold in commercial mixtures. Bioconcentration studies have been performed for each of these herbicides individually, but little information exists concerning long-term exposure to a mixture of these herbicides. The following study examined the uptake of arsenic in crawfish after long-term exposure to this mixture, and the health risks associated with consumption of these crawfish. Bioconcentration and depuration experiments using a 50:50 by concentration mixture of the two herbicides, with and without surfactant, were performed to quantify how much arsenic is concentrated in the edible tissue of the crawfish. Of the three tissues (muscle, gill, and hepatopancreas) sampled hepatopancreas bioconcentrated the highest amount of arsenic. Surfactant significantly reduced this uptake but did not affect bioconcentration of arsenic into other tissues. Surfactant had no effect on depuration of arsenic from any of the tissues. Cooking lowered hepatopancreatic arsenic content, possibly as a result of structural changes in the hepatopancreas. Assessment of the human health risk associated with consuming these crawfish showed an exposure dose at the high end of consumption that was approximately twice the reference dose for arsenic. Cancer risks were averaged at approximately 7 extra tumors in a population of 10,000 and 6 extra tumors in a population of 10,000 resulting from a lifetime consumption of crawfish exposed to the herbicide mixture without and with surfactant, respectively.