Pesticide Toxicity Profile: Chlorophenoxy Herbicides

This document provides a general overview of human toxicity, provides a listing of laboratory animal and wildlife toxicities and a cross reference of chemical, common and trade names of the chlorophenoxy herbicides registered for use in Florida. This document is PI-83, one of a series of the Pesticide Information Office, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date October 2005.

Critical appraisal of a retrospective cohort study

This chapter presents a retrospective cohort study of workers from 10 countries exposed to chlorophenoxy herbicides, assessing cancer mortality. It shows the need for large collaborative international studies, and the methods used. The results are not clearly supported by toxicological and animal experimental evidence, and the question remains open. The critical assessment follows the scheme set out in chapter 10: describing the study, assessing the non-causal explanations of observation bias, confounding, and chance variation; assessing time relationships, strength, dose-response, consistency and specificity, and applying the results to the eligible, source, and target populations; and then comparing the results with evidence from other studies, considering consistency and specificity, biological mechanisms, and coherence with the distribution of exposures and outcomes. The chapter gives a summary and table of the critical assessment and its conclusions; and comments on the impact of the study and research carried out since.

Effects of Chlorophenoxy Herbicides and Their Main Transformation Products on DNA Damage and Acetylcholinesterase Activity

Persistent pesticide transformation products (TPs) are increasingly being detected among different environmental compartments, including groundwater and surface water. However, there is no sufficient experimental data on their toxicological potential to assess the risk associated with TPs, even if their occurrence is known. In this study, the interaction of chlorophenoxy herbicides (MCPA, mecoprop, 2,4-D and dichlorprop) and their main transformation products with calf thymus DNA by UV-visible absorption spectroscopy has been assessed. Additionally, the toxicity of the chlorophenoxy herbicides and TPs was also assessed evaluating the inhibition of acetylcholinesterase activity. On the basis of the results found, it seems that AChE is not the main target of chlorophenoxy herbicides and their TPs. However, the results found showed that the transformation products displayed a higher inhibitory activity when compared with the parent herbicides. The results obtained in the DNA interaction studies showed, in general, a slight effect on the stability of the double helix. However, the data found for 4-chloro-2-methyl-6-nitrophenol suggest that this transformation product can interact with DNA through a noncovalent mode.