Passive sampling and distribution of DDT in air
Pisa, Lloyd Shorai
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Dichloro-diphenyl-trichlorethane (DDT) is a chemical used in malaria control through indoor residual spraying (IRS) and has saved numerous lives in the past six decades. DDT use is restricted/banned under the Stockholm Convention on Persistent Organic Pollutants. Passive air sampling using polyurethane foam was conducted in South Africa to evaluate the presence and trends of DDT and its metabolites. Three sampling sites were used, namely, Barberspan Nature Reserve (rural agricultural), Vanderbijlpark (urban industrial) and Molopo Nature Reserve (isolated nature reserve). Sampling was conducted for a period of one year in 2008. Back trajectories from the three sampling sites were generated using HYSPILT to determine the sources of DDT metabolites to the sampling areas. Forward trajectories were also generated to determine the movement, distribution, and fate of DDT from the areas under Indoor residual spray of DDT for malaria control in South Africa and Swaziland. Chemical analysis was conducted by the RECETOX (Mazaryk University) in the Czech Republic. DDT metabolites (o,p’-DDE, p’p’-DDE, o.p’-DDD, p,p’-DDD, o,p’-DDT p,p’-DDT) were analysed using a GC-ECD (HP 5890). Vanderbijlpark had the highest concentrations of DDT metabolites throughout the year. Barberspan had the second highest concentration and Molopo the least. Seasonal changes in concentration were much the same at the three sites. %p,p’-DDT of ΣDDT is consistent with IRS spraying months in South Africa and Swaziland. A combinations of backward and forward trajectories, together with the temporal pattern of change of the %p,p’-DDT of ΣDDT support the deduction that DDT sampled from the three study sites (to some degree) came from IRS areas in South Africa and Swaziland. The presence of DDT in Molopo Nature Reserve and Barberspan is evidence of long-range transportation over dry semi-desert areas. Back-trajectories indicate the possible source of DDT were the IRS areas in the provinces of Limpopo, Mpumalanga, and KwaZulu-Natal. Some air masses to the sampling sites came from the sprayed areas. The forward trajectories also revealed that the DDT sprayed during IRS could undergo LRT. The DDT metabolites were able to travel to neighbouring countries such as Mozambique, Namibia, Zimbabwe and Botswana.