Plagues and pesticides

This Lancet Neurology article on "Plagues and pesticides" uses Grandjean's recent paper on neurodevelopmental effects to take another angled in the ongoing debate on the balance of benefits of continuing to use DDT in malaria control. 

Steven Goodrick

The recognition of the organochloride pesticide Bis(4-chlorophenol)-1,1,1-trichloroethane (DDT) as a risk factor for developmental neurotoxicity might now finally draw a line under one strand of a debate that has been ongoing for some 70 years.1

DDT was first synthesised in 1874, but it was not until more than 60 years later that the potential of its insecticidal properties was recognised. Commercial sales commenced in 1945, and by 1955 its name had become the byword in agricultural pest control. But its market supremacy was short lived. The backlash against DDT, which started in the late 1960s and early 1970s, was mainly based on ecological concerns and its unknown bioaccumulative effects.2 And by the end of the 20th century DDT was listed as one of the “dirty dozen” persistent organic pollutants regularly targeted for a global ban. It has been spared such a fate only by inclusion as one of the 12 insecticides recommended by WHO in the fight to eradicate malaria, although this endorsement has not been universally applauded.3

DDT has been shown to be toxic in mammals, but the reported adverse effects in humans have mostly focused on the effects of acute exposure and at levels that were far in excess of those encountered in routine insecticidal use.4 There have been reports of the neurological effects of chronic occupational exposure,5 and recently a report on the raised levels of a metabolite of DDT in the serum of patients with Alzheimer's disease.6 However, it is only with the advent of sophisticated epidemiological methods that subclinical toxic effects, particularly during developmentally vulnerable periods, have been studied in depth. Although the question remains as to whether the risks of developmental injury through the controlled use of DDT will outweigh its benefits in the control of malaria in the absence of practical alternatives, at least now the wider spectrum of toxicity of DDT can be appreciated in the debate.

References

1 Grandjean P, Landrigan PJ. Neurobehavioural effects of developmental toxicity. Lancet Neurol 2014; 13: 331-340. PubMed

2 Rogan WJ, Chen A. Health risks and benefits of bis(4-chlorophenyl)-1,1,1-trichloroethane (DDT). Lancet 2005; 366: 763-773.Summary | Full Text | PDF(483KB) | CrossRef | PubMed

3 Ahmad K. WHO's decision challenged. Lancet Infect Dis 2006; 6: 692. Full Text | PDF(43KB) | CrossRef | PubMed

4 Case RAM. Toxic effects of DDT in man. BMJ 1945; 15: 842-845. PubMed

5 van Wendel de Joode B, Wasseling C, Kromhout H, Monge P, Garcia M, Merglier D. Chronic nervous-system effects of long-term occupational exposure to DDT. Lancet 2001; 357: 1014-1016. Summary | Full Text | PDF(188KB) | CrossRef | PubMed

6 Richardson JR, Roy A, Shalat S, et al. Elevated serum pesticide levels and risk for Alzheimer's disease. JAMA Neurol201410.1001/jamaneurol.2013.6030. published online Jan 24. PubMed