Assessment of exposure to DDT and metabolites after indoor residual spraying through the analysis of thatch material from rural African dwellings

Introduction  

We report on the analysis of 4,4′-dichlorodiphenyltrichloroethane (4,4′-DDT) and its metabolites in thatch and branch samples constituting the wall materials of dwellings from South African subtropical areas. This approach was used to assess the exposure to DDT in the residents of the dwellings after indoor residual spraying (IRS) following recommended sanitation practices against malaria vectors.     

Population characteristics of young African women influencing prenatal exposure to DDT (Manhiça, Mozambique)

The concentrations of dichlorodiphenyltrichloroethane (DDT) compounds in cord blood of 214 children born between 2003 and 2006 in Manhiça (Mozambique) have been determined. In this time interval, corresponding to the period before DDT reintroduction for indoor residual spraying, the observed values averaged 0.8 and 0.4 ng/ml for 4,4′-dichlorodiphenyldichloroethylene (4,4′-DDE) and 4,4′-DDT, respectively, and were similar to those found in western countries. However, the 4,4′-DDT/4,4′-DDE ratio was high indicating that the inputs of these compounds arriving to children in utero originated from recent uses of the insecticide. The strongest factor affecting DDT concentration was parity. A well-defined decreasing concentration trend was observed for the cord blood concentrations in the period of study. The trend was also observed for multiparae and primiparae mothers independently. Children from multiparae women showed much lower concentrations than primiparae women. Children from mothers with secondary school level exhibited lower concentrations of these pesticides than mothers with lower degree of education.     

Pyrethroid use-malaria control and individual applications by households for other pests and home garden use

Presence of pyrethroid insecticides in human breast milk and in thatch wall material of dwellings from Southern Africa subtropical area (Manhiça, Mozambique) was investigated to assess potential pyrethroid route of human exposure. Human breast milk samples were collected during 2002 when pyrethroids were widely used as insecticides for mosquito bed nets in Mozambique for malaria control. The median concentration value of total pyrethroids ranged between 87 and 1200 ng/g lw, with λ-cyhalothrin being the most predominant pyrethroid in human breast milk contributing for 35% of the total amount. Moreover, and for the first time, an isomer-specific enrichment was found in human breast milk, showing a selective isomeric accumulation or metabolism in the human body. Based on the calculated pyrethroid concentrations in human breast milk, the daily ingestion rate of pyrethroid was estimated. The nursing infant dietary intake ranged from 0.67 to 9.0 μg (kg of body weight)^− 1 day^− 1. In addition, thatch materials collected after the reintegration of dichlorodiphenyltrichloroethene (DDT) as insecticide residual spraying (IRS) in Mozambique, showed the presence of pyrethroids with concentration values ranging between 6.9 and 700 ng/g dw. In thatch material as well as in human breast milk, pyrethroid contamination was mainly attributed to the agriculture usage of this insecticide knowing that agriculture represent the 80% of the economy in Mozambique. However, a possible usage of this insecticide as IRS in Mozambique cannot be excluded despite their low efficiency for malaria control. The continued use of these compounds (both for agriculture and malaria prevention) and the ingestion rates calculated from the breast milk concentrations indicate that these insecticides cannot be overlooked for the assessment of the lactation risks of breastfeeding infants from the Manhiça region.