Academic journal article Bulletin of the World Health Organization

Malaria Control and Longitudinal Changes in Levels of DDT and Its Metabolites in Human Serum from KwaZulu

Academic journal article Bulletin of the World Health Organization

Malaria Control and Longitudinal Changes in Levels of DDT and Its Metabolites in Human Serum from KwaZulu

Article excerpt

Introduction

The levels of DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane) and its metabolites in serum and whole blood have received considerable attention ([1-5]). Many studies have been conducted in developed countries and have dealt with occupational exposures to DDT ([6, 7]); however, only a few studies have examined people living in dwellings treated with DDT for malaria control purposes ([8, 9]).

Indoor application of DDT is used with great success to interrupt the transmission of malaria parasites in many developing countries. In South Africa it is employed in the northern and eastern Transvaal and northern KwaZulu, where malaria is endemic ([10]). DDT was applied biannually to all homesteads in these areas between 1957 and 1977; subsequently, regular annual applications have been made between January and March.

DDT can accumulate in biological systems because of its stable, lipophilic properties. In KwaZulu the contribution to the burden of DDT in the human body derived from contaminated fish is negligible ([11]), and there have been no significant changes in DDT levels in fish following its application. The mean intake of [sigma]DDT (DDT + its metabolites DDE and DDD) from breast milk by infants in KwaZulu exceeds the recommended acceptable daily intake ([12, 13]). The high levels in mothers' milk have resulted in high levels in infants' blood and are also related to maternal parity and infant age ([14]).

A cross-sectional study, which we reported in 1991, found that serum from 71 people aged [greater than or equal to]3 years living in DDT-treated dwellings in KwaZulu had significantly higher mean levels of [sigma]DDT than that from people in a control area (mean [sigma]DDT: 140.9 [mu]g.[l.sup.-1] and 6.04 [mu]g.[l.sup.-1], respectively; P <0.005) ([9]). For exposed people, the mean [sigma]DDT was significantly higher among 3-10-year-olds than among those aged 20-29 years and 30-39 years (168.6 [mu]g.[l.sup.-1], 60.5 [mu]g.[l.sup.-1] and 84.2 [mu]g.[l.sup.-1], respectively; P <0.05). Statistical analysis suggested that those aged 3-29 years were eliminating DDT (most probably accumulated from contaminated breast milk) faster than they accumulated it. From about 29 years of age, accumulation predominated and the levels began to increase. With regard to the elimination of the metabolite DDE (1, 1 dichloro-2,2-bis(4-chlorophenyl)ethene) and DDT, pharmacokinetic differences between the two age groups have been suggested ([9]). An age-related change in elimination rates was also suggested by the results of a study of DDT applicators ([15]).

The present study was designed to determine longitudinal changes in levels of DDT and its metabolites in the serum of a population protected against malaria by the insecticide, and to examine differences in the rates of change of serum levels of DDT and DDE between younger and older age groups.

Materials and methods

Twelve households, each comprising all the members of a family residing at a specific homestead, were selected in the Mlambongwenya area of Ubombo in northern KwaZulu, where DDT is used for malaria control. At least 10 years' residence at a particular homestead was required for inclusion in the study; homesteads with cement structures were excluded because of the type of DDT formulation applied to them. An inclusion criterion of permanent residence for persons aged [greater than or equal to]3 years was essential because migrant workers were exposed differently.

Two weeks before the initial survey, the informed consent was obtained (in the Zulu language) from participants or, in the case of minors, from their parents, and a questionnaire was completed for each individual. The study design and methods were approved by an ethics committee of the South African Medical Research Council. Local conditions have been described previously ([9]).

Blood samples were collected in November 1986, March 1987, June 1987, and November 1987 by venepuncture and allowed to clot, and 2-ml serum samples were stored in glass vials and frozen on the day of collection. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.