Rising breast cancer rates in Hawaii may be partially attributable to intensive pesticide use, according to a recent study in Environmental Health Perspectives. Breast cancer rates have increased for all racial groups in Hawaii since 1970, but only 30% to 40% of these cancers can be explained by known risk factors.
The study points out that an emerging body of evidence suggests that certain chemicals, including pesticides, play a role in causing the disease by interfering with the body's natural hormone balance.
Over the past 40 years in Hawaii, there has been widespread use of endocrine-disrupting pesticides, including DBCP, DDT, DDE, kepone, heptachlor, chlordane, dieldrin, mirex, lindane and toxaphene.
Exacerbating these hazards, Hawaii is characterised by volcanic soils and heavy rainfall, making it particularly vulnerable to ground water contamination. Because ground water provides a large portion of Hawaii's population with drinking water, the study argues that people living in Hawaii may have experienced unusually high exposures to probable endocrine disruptors.
Compared to other US regions, breast cancer's rate of increase in Hawaii has been high, according to the study. For example, breast cancer incidence among Japanese women in Hawaii increased 42% between 1970 and 1985. Rates in other US areas during the same period did not exceed 20%.
In 1985, both Caucasians and native Hawaiians had rates higher than 200 out of 100,000. The researchers said that breast cancer screening is slightly more common in Hawaii than in other areas of the US, but not enough to explain the higher rates.
The study highlighted several cases in which carcinogens and endocrine disruptors were intensively used in Hawaii, resulting in ground water contamination and human exposure.
For instance, in Oahu, growers regularly fumigated pineapple fields with DBCP until it was restricted in the early 1980s. In 1980, drinking water samples taken from a plantation village in Oahu showed levels of DBCP at 0.01 parts per million, 50 times greater than EPA drinking water standards.
All 738 residents of the village were most likely exposed to DBCP through ingestion and skin contact with contaminated water. Studies later found that this village had a significantly higher rate of abnormal cell growth, including breast cancer, compared to another village eight kilometres away where DBCP was not found in ground water.
Chlordane and heptachlor were also used in Oahu — for agriculture and for termite control in homes. Although banned in the US in 1988, existing stocks of the chemicals in Hawaii could still be used, and as recently as 1993, heptachlor was applied to pineapple fields in Oahu by Del Monte.
According to the study, chlordane and heptachlor cause cancer, harm the immune system and may be endocrine disruptors. They remain biologically active for decades.
During a 15-month period in 1981 and 1982, many dairy cattle in Oahu were accidentally fed pineapple leaves containing heptachlor residues. As a result, the local milk and dairy supply remained contaminated for years. Between 1981 and 1984, the legal standard for heptachlor residues in food (0.3 ppm) was exceeded 10-fold in milk and dairy products supplied by local dairies.
Follow-up investigations found that the breast milk of women who had consumed local dairy products contained heptachlor at levels averaging 200 ppm — some cases exceeded 400 ppm.
The study says that other researchers compared heptachlor levels in human milk among US regions and reported that levels in Hawaii were 20% higher than in south-eastern states and 65% higher than in north-eastern states.
[From Pesticide Action Network North America Updates Service.]