|health & fitness|
Herbicides Cause Birth Defects
||Every spring, Midwest farmers apply 150 million pounds of herbicides and pesticides to their crop fields, and spring rains wash a large amount of those chemicals into the drinking water supply. During periods of peak runoff in May to August, every day up to 18,000 pounds of chemicals flow down the Mississippi River into the Gulf of Mexico. The contamination of drinking water with these chemicals is a serious public health issue, because none of the chemicals are removed by the drinking water treatment technologies used by more than 90% of all water utilities in the United States. It's exactly the same story in Canada.|
It is no wonder then that this recent study by D.M. Schreinemachers has found that the incidence of birth defects among among newborns was between 60% to 90% higher in counties with high wheat production than in counties with low wheat production. Birth defects ranged from the respiratory and circulatory systems to defects of the musculo-skeletal system like clubfoot, fused digits and extra digits.
Also, infant death due to congenital abnormalities was higher in boys born in counties with high wheat production compared to boys in counties with low wheat production. Most of the infant boys' deaths were caused by heart and musculo-skeletal birth defects.
The bitter irony is that all these poisons are not necessary. We can have a completely poison free, far more productive, far cheaper, and far healthier agriculture - as described in these pages. Meanwhile, the bitter agony and heartbreak will continue as increasing numbers of our newborns either die shortly after birth, or are marred and disfigured for all of their lives.
Birth Malformations and Other Adverse Perinatal Outcomes in Four U.S. Wheat - Producing States.
In a study comparing the rates of birth defects counties where wheat is grown abundantly to places where it is not, Schreinemachers concludes that herbicides used on wheat may be causing birth defects. Babies born in wheat growing areas of the US west are more likely to have several types of birth defects than babies born in the same region but where wheat is less common.
While the study falls short of proving causation, it is consistent with earlier research on animals and with people indicating that a family of herbicides commonly used on wheat, the chlorophenoxy herbicides such as 2,4-D, disrupt fetal development.
What did she do? Schreinemachers analyzed the incidence of birth defects in 147 rural counties in 4 states, comparing rural regions of high wheat production with rural regions of low wheat growing. Two chlorophenoxy herbicides, 2-4,D and MCPA, are used heavily on wheat, much less so on crops like soy which dominate the counties where wheat is less abundant. Hence by comparing high wheat and low wheat production counties, Schreinemachers sets up a comparison of high chlorophenoxy exposure versus low exposure.
The study focused only on Caucasian singleton (not twin) children born to mothers at least 18 years old. Data for the comparisons was obtained from health records maintained in the National Center for Health Statistics. In all, records for 43,634 births in the counties of interest from 1995 to 1997 were analyzed.
What did she find? Birth outcomes differed significantly in several ways: Birth defects of the respiratory and circulatory systems were greater in high wheat production areas, as were defects of the musculo-skeletal system like clubfoot, fused digits and extra digits. These birth defects were 60% to 90% more likely in high wheat production counties. The odds-ratios for these increases were all significant.
The chances of birth defects rose for babies conceived in the spring, when herbicide spraying was most intense. Boys born in April - May in high wheat production counties were almost 5 times more likely to have a birth defect than boys born in low wheat counties at other times of the year.
Infant death due to congenital abnormalities was higher in boys born in high wheat production counties compared to boys in low wheat production counties. Most of the infant boys' deaths were caused by heart and musculo-skeletal birth defects. No comparable elevation in risk of infant death was seen for girls.
What does it mean? Epidemiologists in general agree that 'ecologic' studies like Schreinemachers' - examining geographic patterns to highlight statistical associations - stop short of demonstrating causation. Instead they are one piece of evidence that can be considered along with parallel studies using other techniques, all approaching the question of human impact from different directions. Indirect work like this is necessary because purposeful experimentation on humans to determine, for example, whether an herbicide causes birth defects, would be unethical.
Schreinemachers work neatly sidesteps a common weakness of ecologic studies of the effects of agricultural pesticides by focusing all of her analysis on rural communities. Comparisons are often made between rural and urban residents; these studies unavoidably add a raft of confounding variables due to the differences in urban versus rural environments, health care, etc.
But by comparing people living in different rural counties, varying in the intensity of wheat growing, Schreinmachers doesn't avoid all confounding variables. Two stand out: first, some wheat is grown in the low wheat counties, and thus some, albeit reduced, exposure to chlorophenoxy herbicides will take place. Second, other types of herbicides can be used heavily on the crops grown instead of wheat, for example, atrazine on corn.
Neither of these considerations would bias Schreinemachers' analysis toward showing a link between chlorophenoxy herbicides and birth defects. If anything, they would have decreased her chances of finding a positive result, by increasing the numbers of birth defects in low wheat counties. The ideal comparison would have been rural counties with no agriculture versus. high wheat production, but rural counties with no agriculture within the region are rare at best.
Hence the fact that Schreinemachers found heightened risk of birth defects for several comparisons needs to be taken seriously, even more so because the weight of evidence from other studies strongly links chlorophenoxy herbicides with birth defects. Notable amidst earlier work are studies showing higher birth defect rates in Minnesota, New Zealand and Norway associated with chlorophenoxy exposures, and experimental studies in showing that chlorophenoxy herbicides cause birth defects in rodents. [Schreinemachers, DM. Environmental Health Perspectives 111:1259-1264. 2003.]
References: Hanify JA, Metcalf P, Nobbs CL, Worsley KJ. 1981. Aerial spraying of 2,4,5-T and human birth malformations: an epidemiological investigation. Science 212:349–351.
Kristensen P, Irgens LM, Andersen A, Bye AS, Sundheim L. 1997. Birth defects among offspring of Norwegian farmers, 1967–1991. Epidemiology 8:537–544.
Schardein JL. 1993. Chemically Induced Birth Defects. 2nd ed.New York:Marcel Dekker, Inc.
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