Authors
Dalvie, M., Myers, J., Thompson, M., Robins, T., Dyer, S., Riebow, J., Molekwa, J., Jeebhay, M., Millar, R., and Kruger, P.

Title
The long-term effects of DDT exposure on semen, fertility and sexual function of malaria vector-control workers in Limpopo Province, South Africa.

Journal
Environmental Research. 96: 1-8. 2004.

Summary
Epidemiologic evidence suggests that male reproductive function is deteriorating over time. There have been reports of reduced semen quality, and increasing incidence of testicular cancer, cryptorchidism and hypospadias in many regions of the world. Natural and synthetic endocrine disrupting chemicals have been implicated in the deterioration of male reproductive health because of their ability to mimic the effects of natural hormones. DDT (dichlorodiphenyltrichloroethane), a pesticide which is widely used for malaria control in developing countries, is thought to be capable of inducing such hormonal effects, thereby disrupting normal physiological processes.

Dalvie et al. conducted a cross-sectional study of 60 workers of the Malaria Control Center (MCC) in a province of South Africa, in order to assess the long term reproductive effects of DDT. Physical examination of the reproductive system and semen analysis were conducted to assess parameters of reproductive function. A questionnaire was also administered to obtain information about sexual function, reproductive history, and employment history.

Sperm count, density, and motility using the World Health Organization (WHO) criteria and morphology using the Tygerberg criteria were determined. Sixty percent of the samples were below the standard for semen volume and 41% of samples were below the standard criteria for sperm count. Morphology scores were especially low, with 84% of the samples falling within the sub-fertile range. Abnormal testis disposition was the most prevalent genital abnormality detected upon physical examination, this was found in 71% of the subjects. Participants were asked to report if they experienced any of the following sexual problems: lack of interest in sex, difficulties in full erection, early ejaculation, and inability to ejaculate. Response to each of these self-perceived problems ranged between 10% and 20%. There were no statistically significant associations found between these symptoms of sexual dysfunction and measures of DDT exposure after adjusting for age and education. Multivariate regression analysis was used to measure the association between DDT levels and semen parameters. Sperm density was significantly associated with serum DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene) levels, a component of DDT, while sperm count was negatively associated with DDT.

The overall semen quality was below normal according to the standardized criteria. However, the authors suggest that the criteria used to assess semen morphology may have been inappropriately strict for the purposes of this study. There were few statistically significant associations between semen parameters and measures of exposure. The only semen parameter negatively associated to DDT exposure was reduction of sperm count. The authors propose that this is a biologically plausible relationship as DDT compounds have been shown to have an anti-androgenic effect, which can cause a decline in sperm count due to inhibition of testosterone action at target tissues. However, no previous epidemiological study has found that DDT has an effect on semen. The lack of association between DDT measures and other sexual parameters suggests that factors besides DDT may be responsible for the lower than normal overall semen quality in this study population. One of the limitations of a cross sectional study is that there are no external controls. Comparison of these findings to men residing in the area who are not occupationally exposed to DDT may reveal other factors which are related to these outcomes.