DDT: Summaries of Recent Epidemiological Studies

Paper 1: Impaired Semen Quality Associated with Environmental DDT Exposure in Young Men Living in a Malaria Area in the Limpopo Province, South Africa (Aneck-Hahn et al. 2007)

In this study, the defined population was healthy, non-occupationally exposed men from three villages in Limpopo Province, South Africa. Researchers held information sessions in the villages to recruit volunteers, who were given a questionnaire to assess whether they fit the inclusion criteria of age, health, and residency location. Participants accepted into the study had no history of testicular trauma, orchitis, urinary infection, sexually transmitted disease, use of hormonal medication, or known exposure to gonadotoxins, or neuropsychiatric disorders. All men accepted were between ages 18 to 40 years, and had been living in the communities for at least one year, and were not aware of any occupational exposure to DDT (ie, they did not work with DDT in farming or malaria control jobs).

The exposure of interest was DDT due to malaria-control spraying activities. Study participants provided information through the questionnare on the sprayed status of their homes and on potential confounding variables like diet, fertility history, and potential spermatotoxic exposures like heat, radiation, physical trauma, STDs, urinary tract infections, and chemical pollutants including smoke and alcohol. Additionally, blood samples were collected from each participant and analyzed for concentrations of the DDT metabolite compounds p,p’-DDT and p,p’-DDE. As the outcome of interest was reduced semen quality, semen samples were obtained by each participant. Physical characteristics of the semen (viscosity, liquifaction, volume, pH) and biological characteristics (sperm motility, leukocytes presence) were analyzed.

Paper 2: DDT and Urogenital Malformations in Newborn Boys in a Malarial Area (Bornman et al. 2010)

The defined population was newborn boys in the Vhembe District Municipality of Limpopo Province, South Africa. During a two-year period of 2004-2006, there were 7146 babies born in Tshilindzini Hospital, the district hospital. Inclusion criteria used to narrow down this population were the sex of the child, birth mass, and the residency location of the mother. Of the 7146 newborns, 3310 fit the inclusion criteria.

The exposure of interest was in utero exposure to DDT from indoor residual spraying.  This was assessed by using the Malaria Control Programme’s provided information on spray status in the villages where mother’s reported they lived. Mothers (and therefore their child) were classified as being from a currently sprayed village (sprayed during the time of the study and presumably during or around the time the mother was pregnant), a historically sprayed village (1995-2003), or a village that had never been sprayed. An important note is that malaria spray records were not available for the period of 1980-1994. Therefore, a “never sprayed” village was known officially to not be sprayed during the period of 1945 – 1979 or 1995-2003, but potentially could have been sprayed during the 1980-1994 period. The mothers were also asked questions about how many years they had lived in that village and what their occupation was, to assess relative lengths of in-home exposure to DDT. They were also asked about their smoking history, drinking habits, age, and tribal ethnicity, in order to explore potential cofounding variables that might be considered to lead to a spurious correlation if not addressed. 

The outcome of interest was defined as urogenetial birth defects. The authors state that “assuming that at least some of these endpoints have a common cause due to endocrine alterations, and to increase the power, they were grouped as ‘any UGBD’ variable. All urogenital malformation variables were analysed as being either present or absent.” Trained nurses examined newborns for the following six malformations: micropenis, cryptochidism, hypospadias, chordee, phimosis, and penile cysts.

Paper 3: Reduced Seminal Parameters Associated with Environmental DDT exposure and p,p’-DDE Concentrations in Men in Chiapas, Mexico: A Cross-Sectional Study (De Jager et al. 2006)

In this study, researchers addressed the question of endocrine-disrupting effects of environmental DDT exposure from malaria control. The study population was men from six rural communities in Chiapas, Mexico, an area that used indoor spraying of DDT one or two times per year to control malaria, until 2000. 116 volunteers met the inclusion criteria of aged between 18 to 40 years with no history of diagnosed infertility, testicular trauma, urinary infection, STDs, use of hormonal medications, exposure to known gonadotoxins, use of sauna baths, or history of neuropsychiatric disorders (which are potential confounding variables).

In addition to the inclusion criteria of living in a historically sprayed village, real-time exposure levels were assessed by analyzing blood samples for the presence of the DDT metabolites. The outcome of interest was poor semen quality, measured by analyzing physical and biological characteristics of semen samples from each participant.

 

Paper 4: In Utero Exposure to the Antiandrogen 1,1-Dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) in Relation to Anogenital Distance in Male Newborns from Chiapas, Mexico (Longnecker et al. 2007)

This study was based on the hypothesis that in utero exposure to DDE (a DDT metabolite) decreases anogenital distance in newborn males (a physical response outcome of the antiandrogen activity of DDE). The study population of newborn boys was recruited into the study through recruiting mothers during the postpartum period at two city hospitals in Chiapas, Mexico. Exclusion criteria were that the mother was over 35 years old, the pregnancy was considered “complicated” from a medical standpoint, or the mother had pregnancy-related diabetes, hypertension, or a seizure disorder that required medication. Mothers with history of urinary tract infections, psychiatric, kidney, or cardiac disease, or who did not speak Spanish were also excluded. Finally, newborns included in the study were males with gestational periods over 36 weeks and birth weights over 2.5kg. In total, 781 mother-infant pairs were enrolled in this study.

Exposure was determined based on maternal serum levels of DDE and DDT. Outcome measurement was through measurement of anogenital distance and penis size. Measurements were taken within 6 hours of birth for over 80 percent of the newborns. The remaining newborns’ measurements were taken within 34 hours of birth, with one exception that was 7 days post birth.

 

Paper 5: Long-term Effects of DDT exposure on semen, fertility, and sexual function of malaria vector-control workers in Limpopo Province, South Africa (Dalvie et al. 2004)

This study looked at 60 men who were occupationally exposure to DDT. Malaria control workers responsible for spraying homes with DDT were recruited from three work camps in Limpopo Province, South Africa. A questionnaire was used to collect information on demographics, work history, medical history, and sexual function and reproductive history, as well as use of alcohol, tobacco, and cannabis, in order to explore potential confounding variables. Exposure was defined through the occupation, and was measured by the presence of six different DDT metabolites in the blood. Outcome was measured through analysis of physical and biological semen quality parameters.

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