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Chapter 1. Health Effects of Herbicides

Weed Killers By The Glass: Chapter 1. Health Effects of Herbicides

September 1, 1995

The pesticides most frequently detected in drinking water -- the triazines and the acetanilides -- cause a litany of health effects, including cancer, birth defects, and disruption of the endocrine (hormone) system. The triazine herbicides (atrazine, cyanazine, simazine) cause mammary gland cancer in repeated studies in female rats through interference with the normal functioning of the hormone system. In press statements announcing its regulatory review of the triazines in November, 1994, EPA cited the possible relationship between triazine exposure and the increased rate of breast cancer in women as a reason for formal review of these weed killers (EPA 1994). Cyanazine is also a reproductive toxin, causing heritable genetic mutations in a number of tests, and birth defects in rabbits and rats.

The acetanilide herbicides (alachlor, acetochlor, metolachlor) cause a rare nasal turbinate cancer in animals. This cancer was initially classified as brain cancer, but was reclassified as nasal turbinate cancer after numerous industry appeals. Alachlor causes this rare cancer even when the animals are exposed only for the first six months of their lives, suggesting that infants may be at higher risk when they are exposed to alachlor in formula and juice reconstituted with alachlor-contaminated tap water. Two of the acetanilide herbicides, alachlor and the recently registered acetochlor, are classified by EPA as probable human carcinogens. Alachlor has also been found to disrupt the endocrine system.

On October 17, 1994, the day before the release of Tap Water Blues, EPA Administrator Carol Browner denied a request by Ciba, the manufacturer of atrazine, to allow seven times more atrazine in drinking water (21 parts per billion) than allowed by the current standard (3 parts per billion). In her letter to Emilio Bontempo, the president of Ciba, Administrator Browner affirmed several of the core recommendations of Tap Water Blues. In particular, EPA confirmed the need to look at the triazines as a toxicological group, and concluded that current standards may not adequately protect the public from cancer risks due to atrazine alone or the triazine herbicides when considered together. The letter noted that:

 

"We are also considering whether to regulate the chlorotriazines (i.e. atrazine, cyanazine, simazine) as a group rather than regulating atrazine alone. The triazines have similar structure, mode of action, toxicity and degradates. We presently do not account for the potential additive increase in cancer risk due to exposure to the components of the chlorotriazines mixture, and therefore may be understating risks when regulating the contaminants individually" (Browner 1994). Adding further that: "...the Agency may have underestimated the risk from atrazine exposure in drinking water...."

One month later, in November 1994, the EPA took another step towards reducing exposure to pesticides in drinking water, announcing that they were beginning a special regulatory review of the triazine herbicides. This marked the first time that the agency had ever undertaken a regulatory review of more than one pesticide at a time, and the first time that it would base the risk assessments in the review on additive exposure to the three different active ingredients -- the chlorinated triazine herbicides atrazine (see Sidebar 1), cyanazine, and simazine.

The Special Review was precipitated by the agency's concern over widespread drinking water contamination and risks faced by farmers and commercial applicators of the herbicides. In announcing the review, the Agency noted that it was particularly concerned over the cancer risks from exposure to the triazine herbicides because of possible links between the mammary tumors in female rats and breast cancer in women. The EPA press statement indicated at that time that, "While the EPA does not have information which supports the link between exposure to the triazine herbicides and human breast cancer, the Agency cannot dismiss the possibility that an association could exist" (EPA 1994).

 

Cyanazine Phase-out

On August 2, 1995, nine months after the announcement of the special review, the EPA and Dupont Agrichemical Company announced the phase-out and ultimate ban of the triazine herbicide cyanazine. Under the agreement, Dupont, the sole producer of cyanazine, will cancel the registrations of all cyanazine products on Dec. 31, 1999. Prior to that date application rates will be reduced to encourage a gradual transition to substitute products. Existing stocks of the weed killer will be allowed to be used through Dec. 31, 2002.

In announcing the ban, Dupont cited concerns about the cost of battling the ongoing EPA review of the triazines, as well as EPA's concerns about the cancer risks that cyanazine presents to the public and pesticide applicators. Implicit in the ban is Dupont's recognition that the EPA considers cyanazine a high risk compound and that the agency would aggressively pursue stiff regulation of the herbicide. The decision also signals Dupont's recognition that it might lose the fight with EPA because cyanazine is in fact a highly toxic substance that presents unacceptably high risks in drinking water. Plainly, the company did not consider the battle a wise use of resources. To replace cyanazine, Dupont will aggressively market new, sulfonylurea (SU) products as safer more effective alternatives to cyanazine. These chemicals are toxic to weeds and other plants via enzymes that do not exist in mammals. Consequently, they are far less toxic to humans than the triazines. They do not contaminate water supplies and are applied only after weeds are present, a factor that encourages more selective weed control practices. SU's however, are extremely toxic to some non-target plants and must be applied with great care. Nonetheless, increased use of the SU's paves the way for a broader phase-out of other triazines and other herbicides that contaminate drinking water throughout the Midwest.

 

Drinking Water Standards Do Not Adequately Protect Public Health

Under the Safe Drinking Water Act, EPA sets enforceable standards for allowable levels of pesticides in drinking water, and requires water utilities to monitor for these contaminants. Standards are set as a two part process. First, the EPA sets a non-enforceable Maximum Contaminant Level Goal (MCLG), based purely on health considerations. These MCLGs are set at levels "at which no known or anticipated adverse effects on the health of persons occur, and which allows an adequate margin of safety." The agency then sets enforceable standards, known as Maximum Contaminant Levels (MCLs), which are based upon the MCLGs, but are usually adjusted to ensure that they are technically and financially feasible. For a number of reasons, standards for the herbicides commonly found in drinking water -- atrazine, cyanazine, acetochlor, alachlor, and metolachlor -- fail to adequately protect public health.

 

Drinking water standards allow excessive cancer risks.

Because of an outdated methodology used to set drinking water standards for these chemicals, they allow 10 to 30 times greater cancer risks than EPA's Office of Pesticides allows for the same pesticides in food. Thus, even when pesticide contamination levels are within EPA's drinking water standards, they may still pose cancer risks that exceed the federal governments "negligible" (See Note 1.) risk standard by a factor of 10 or more.

 

Standards do not take the risk of exposure to multiple pesticides or pesticide metabolites into account.

Water supplies are often contaminated by multiple pesticides, and this study shows that a single glass from the tap can contain up to nine pesticides or metabolites. In the case of the triazine herbicides -- which, according to EPA all act by the same toxicological mechanism -- multiple exposures can significantly increase health risks. Unfortunately, the standard setting process makes the unrealistic assumption that we are always exposed to pesticides in isolation, never more than one at a time.

 

Standards fail to protect children.

After a five-year study, the National Academy of Sciences concluded in 1993 that because of differences in physiology children are usually at greater risk from pesticides than adults. On top of this, they are exposed to higher amounts of pesticides relative to their size. For example, infants drink more than twice as much water per unit of body weight than adults, meaning that they receive more than twice the exposure to toxic agents in drinking water. Since the release of the NAS study, no drinking water standard has been set or adjusted specifically to protect infants or young children.

 

Safe Drinking Water Act monitoring requirements are inadequate.

The Act only requires water utilities to test their water once every three months for these herbicides (and many other contaminants). This quarterly monitoring is an ineffective measure of contamination for seasonal contaminants like the herbicides found in this study, which have peak runoff periods in the spring and summer. Under the current quarterly monitoring scheme, water utilities are able to avoid peak contamination periods during May, June, and July. As a result, utilities that are performing all required testing often significantly underestimate the levels of these herbicides in their drinking water.

 

Enforceable standards do not even exist for some pesticides.

EPA has set enforceable drinking water standards (MCLs) for three of the pesticides of primary concern: atrazine, alachlor and simazine. For the three other major herbicide contaminants, cyanazine, metolachlor, and acetochlor, EPA has yet to set enforceable drinking water standards. (See Note 2.) Instead, the EPA has issued non-enforceable Lifetime Health Advisories (LHAs). Consequently, water utilities are not required to test their water for these pesticides, and if they do test they are not required to inform their customers if the chemicals are found at levels that exceed federal health advisories.

Congressional Action To Weaken the Law

Just as EPA has begun to address some of the important shortcomings of the current standard setting process, and ensure that public health is protected, Congress is acting in numerous ways to derail these efforts and weaken current law. As this report goes to press, there are ongoing efforts in Congress to:

 

Weaken pesticide law, making it more difficult for EPA to keep triazine herbicides from contaminating tap water.

On June 19 the House Agriculture Committee passed HR 1627, a sweeping rollback of current pesticide laws supported by the pesticide and agriculture industry, as well as sellers of fruit and vegetables. Among other setbacks, this bill would make it far more difficult for the EPA to restrict or ban the use of any pesticide in order to protect public health.

 

Weaken the Safe Drinking Water Act, making it more difficult for EPA to set adequate health standards and ensure that affected water utilities are testing their water for herbicide contamination.

Senator Dirk Kempthorne (R-ID) has circulated draft legislation supported by water utilities that will relax health standards and monitoring requirements for chemicals in drinking water, including these herbicides. Representative Thomas Bliley (R-VA) the chairman of the House Commerce Committee, is expected to introduce similar legislation to weaken the Safe Drinking Water Act in the House of Representatives.

 

Defund EPA's Special Review of the triazines.

The non-binding resolution accompanying the May budget approved by the House Budge committee specifically cites the EPA review of atrazine as a "Federal Mandate that Warrants Elimination or Reform." And Representative David McIntosh (R-IN), has included the triazine special review on a list of regulations that need to be "captured or stopped," by possible actions in the House of Representatives.

 

The FY 1996 appropriations bill passed by the House of Representatives would delay or undermine much of EPA's ability to remove weed killers from tap water.

The bill cuts the EPA budget by one-third, effectively short-circuiting the Agency's ability to set and enforce standards for pesticides in drinking water, or to continue the special regulatory review of the triazine herbicides. The bill eliminates a $1.8 billion revolving fund set up specifically to help smaller communities treat contaminated drinking water as it abolishes the EPA's monitoring program and holds up $100 million in grants given to states and communities used to minimize water pollution by runoff such as herbicides.