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 Called "economic poisons" by the state Department of Pesticide Regulation, herbicides are chemical poisons designed to kill plants by upsetting fundamental biological processes. Thousands of recorded injuries and laboratory studies have demonstrated that herbicides regularly cross ecological and biological boundaries to damage non-target organisms. Yet in spite of their poisonous nature and widespread use, health and environmental data are incomplete for virtually every herbicide formulation.
The chart with this section describes some of the known and suspected toxicological effects of eight herbicides used in the greatest quantities on California's roadsides. Associated with an array of human health disorders, these chemicals actually represent only a portion of those routinely sprayed onto California's roads.
For this chart, herbicides are compiled, named and described according to the active (directly herbicidal) ingredient shared in common by various formulations. This method was used because the identity of many of the other chemicals in formulations - called inert ingredients - are kept secret by manufacturers and regulatory agencies. The percentage of active ingredient contained in these mixtures is described on the chart in the proportions in which each appears in herbicide formulations.
Diuron, for example, is the active ingredient of several formulations - Karmex, Karmex DF, Krovar, Krovar 1 DF, Diurex 80 DF, Diurex 4L, Diuron FL - used on California thoroughfares. The portion of diuron in these formulations ranges from 40% to 80%. The identity of the 20% to 60% of the formulations' ingredients is a secret; chemical manufacturers conceal from the public the names of many chemicals in their formulations, and they are supported by state and federal agencies in this subterfuge. The information that is publicly available about inert ingredients, however, indicates that the majority are biologically active and toxic, often as much as are the active ingredients or, in some cases, even more so.
What We Do Know
The information that is available about the toxic effects of many of the chemicals used on California's roadsides has been learned in studies conducted by the manufacturers of the chemicals. These studies, done to satisfy requirements of federal and state governmental agencies, have characterized the more egregious potential hazards of the active ingredients.
Experiments to determine the effects of herbicides on human subjects is considered unethical and tracing their impacts in accidentally exposed humans is prohibitively expensive when not impossible. Instead, toxicological tests are conducted on animals. Rats, mice, rabbits, and beagle dogs are exposed to chemicals in a laboratory setting for studies designed to satisfy governmental requirements for certain information.
As a result of these studies, regulatory authorities and scientists have recognized a potential for herbicides most commonly used on California thoroughfares to cause illnesses to humans. These adverse health effects include: cancers (diuron, oxadiazon, simazine, norflurazon, oryzalin, isoxaben, bromacil); reproductive and development disorders (diuron, oxadiazon, norflurazon, bromacil); liver toxicity (diuron, glyphosate, oxadiazon, simazine, norflurazon, oryzalin, isoxaben); kidney toxicity (glyphosate, oxadiazon, simazine, oryzalin); blood disorders (diuron, simazine, norflurazon, oryzalin) and other adverse health effects.
Uncharted Territory
Unfortunately, what we know about these herbicides is dwarfed by what we don't know. Despite the dangers, tests for many potential toxicological effects of herbicides are not required until overt examples of negative reactions are recorded over a long period. After that, it still takes decades to plan, initiate and carry out investigations. Most have never been completed.
Toxicological studies are not required for the effects of herbicides on:
children, although it's well established that they are more vulnerable to injury from biologically active chemicals such as herbicides. Chemicals considered to be moderately toxic can be highly disruptive to children because they constantly grow new cells, their bodies metabolize substances quickly and they are much smaller than adult males for whom chemical exposure standards are set. Many scientists believe that rising cancer rates among children are due to exposures to chemicals. As a result, the EPA is setting standards for how much herbicide residue children can eat, but ignoring exposures that may occur as a result of roadside spraying. Even oxadiazon, which is described under California's Proposition 65 as a chemical known to cause cancer and birth defects, is not prohibited from use where children travel.
individual sensitivity, a condition which makes some people more susceptible than others to the negative effects of certain chemicals. Anyone who has an inherited inability to produce certain enzymes that detoxify chemicals, for example, may be more susceptible to the toxic effects of glyphosate, which has been found to depress certain other detoxification enzymes. Diuron, norflurazon, and oryzalin, have been shown to affect blood and blood-forming tissues and may be especially dangerous for persons with inherited blood abnormalities or acquired blood diseases. It was found in a study conducted by the California Department of Health Services that almost one in twenty Californians exhibit symptoms of chemical sensitivity.
endocrine disruption, or alteration of the regulatory system for hormones that rules every function of the body. Endocrine-disrupting chemicals such as bromacil often affect reproductive processes and can be especially dangerous to fetuses and young children. This is of particular concern to scientists because of the threat to future survival of humans and other species.
immune system depression has been shown to occur at greater rates in agricultural areas where herbicide use is concentrated. A poorly functioning immune system is the cause of increased infectious disease and can directly contribute to the promotion of cancer and other health effects simply because the body's defense mechanisms cannot function to promote optimum health.
Other chemicals such as inert ingredients or products of the break-down of herbicide chemicals are poorly understood. These include:
inert ingredients - the identity of which is kept secret from the public by manufacturers and government agencies but are nevertheless often highly toxic, sometimes even more toxic than the better characterized active ingredients. The surfactants mixed with the active ingredient glyphosate, for example, can be many times more toxic to humans than glyphosate itself. These surfactants cause severe skin, eye and respiratory harm while glyphosate itself does not share these toxicological effects.
contaminants - inadvertent waste products of chemical manufacture that cannot be removed from herbicide ingredients. These chemicals can be extremely hazardous, as in the case of 3,3,4,4-tetracholorazobenzene (TCA), a contaminant of diuron which is similar in structure and function to 2,3,7,8-TCDD, the most potent of the dioxins, or as in 1,4-dioxane, a potent liver carcinogen and contaminant of glyphosate.
metabolites and degradants - chemicals formed when herbicides break down in the environment due to mechanisms involving soil microorganisms, sunlight, heat and other processes. These secondary chemicals are often of equal or greater toxicity than the original parent chemical. When glyphosate is metabolized, for example, it becomes formaldehyde, recognized as a human carcinogen under California's Proposition 65.
chemical interactions such as synergism - effects created as a result of mixing chemicals together. Glyphosate and polyethoxethyleneamine - which are mixed together in the most popular roadside herbicide formulations - are about three times more lethal when tested in combination as when each ingredient is tested alone. Research on chemical blends like those in herbicide formulations is limited to lethal effects and acute eye and skin effects of formulations. No studies are done of mixtures of two or more formulations, and the added surfactants, regularly used on California's roads.
The potential for harm caused by these herbicides makes their use by government agencies on roads where millions of people travel each day a highly questionable activity. Caltrans recognized the gravity of this problem when it pledged to reduce its use of roadside chemicals by 50% by the year 2000. Unfortunately for Californians, by its own figures, it's clear that Caltrans will not fulfill this promise.
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