Longnecker, MP, MA Klebanoff, H Zhou, JW Brock. 2001. Association between maternal serum concentration of the DDT metabolite DDE and preterm and small-for-gestational-age babies at birth. The Lancet 358: 110-114.
Longnecker et al. demonstrate a powerful association between DDE levels in mothers' serum and the likelihood of premature birth. The higher the contamination level, the more likely was preterm birth. They also show that contamination is linked to the baby's size, with babies more likely to be small for their gestational age when born to mothers with higher DDE levels.
According to the lead author, in the US in the 1960s there may have been "an epidemic of pre-term births that we are just now discovering."
In the Lancet paper, the authors write that their results
| " strongly suggest that DDT use increases preterm births, which is a major contributor to infant mortality. If this association is causal, it should be included in any assessment of the costs and benefits of vector control with DDT." |
Interviewed by the British science magazine, New Scientist, Dr. Matthew Longnecker (US National Institute of Environmental Health Sciences), the lead author of the report, estimated that DDT use in the United States could have been responsible for as much as 15% of infant deaths during the 1960s.
What
did they do?
Longnecker et al. analyzed data and samples from a prospective
study conducted of the causes of neurological disorders and other conditions
in children born to mothers pregnant in the US between 1959 and 1966 (Niswander
and Gordon 1972). The data were compiled in the US Collaborative Perinatal
Project (CPP) , which enrolled some 42,000 women over that time span and
evaluated 55,000 babies. Of the total sample of women participating, the
vast majority deposited sufficient serum into a bank to allow subsequent
measurement of DDE levels. Details of the sampling are available in the
paper.
Longnecker et al. measured concentrations of p,p'-DDT and p,p'-DDE in serum samples taken from the pregnant mothers. They then evaluated the DDE concentrations in relation to the chances of a pre-term birth and infant size (controlling for gestational age).
What did they find?
- The
likelihood of preterm birth increased steadily with increasing concentration
of DDE in the mother's serum
(p < 0.0001). - The likelihood of the baby being small for its age was highest for babies whose mother had the highest DDE concentration). Similarly, the chances of a baby weighing less than 2500 grams (or 5 pounds, 8 ounces) increased dramatically with increasing DDE concentration. The highest levels of DDE increased that likelihood by over four-fold. (p < 0.0001).
- The authors were able to detect the onset of these DDE impacts at a concentration of 10 micrograms/liter.
What
does this mean?
DDE blood levels in the US are now well beneath those concentrations detected in this study (made of blood samples obtained in 1959-1966) and beneath the apparent threshold for the effect detected in the authors' statistical analysis (10 micrograms/liter). Hence even though DDE contamination persists in people in the US, similar studies today in the US would be unlikely to detect an effect. This is not the case, however, in countries where DDT continues to be used for insect control.
According to the authors:
| "In tropical countries, where DDT is used for malaria control, blood concentrations of DDE can greatly exceed the range observed" in the sample they studied. If DDE causes premature birth, it is likely to cause increased infant mortality. |
They go on to observe that "Benefits of vector control with DDT might need to be reassessed in the context of this adverse effect on human beings and the availability of alternative methods of vector management." This is a cautious way of stating that DDT's potential contribution to infant mortality should be factored into decisions about phasing out DDT use, increasing the urgency of finding safe and affordable alternatives.