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Water
Each year the Department of Pesticide Regulation and several other agencies take samples from selected California wells. These samples are then analyzed for the presence of certain pesticides called "leachers" because they percolate through soil to pollute ground water. DPR then publishes a summary of the results, as required by the Pesticide Contamination Prevention Act. And year after year, as the summary shows, the same herbicides contaminate well water.
Of the six herbicides most commonly reported to be detected in wells, three are among the top chemicals used to kill weeds on our public roads. In the most recent survey, another top roadside herbicide was added to the list, though its detection came as a surprise to pesticide regulators.
Norflurazon - which was on a low-priority sampling list in California because it was not anticipated to pollute groundwater - was found in groundwater by Florida which is more vigilant about water quality because the state is experiencing a water pollution crisis. California found norflurazon - the third most popular herbicide used on the state's roadsides - in 9.5% of the wells in 1997, the first time samples were taken.
For one roadside weed killing chemical, simazine, samples were analyzed for the chemicals to which it degrades, because these breakdown products are well known to be persistent and toxic water polluters. According to the most recent survey, simazine was found in well water samples 74 times and its two breakdown products were detected a total of 64 times.
When herbicide leachers were first found polluting the state's groundwater over a decade ago, Californians were shocked and dismayed. Legislation and the enactment of regulations gave the impression that the problem was under control. That is not the reality, however. The most popular herbicide used by public road agencies is still diuron, which has been found in many wells each year since sampling began fourteen years ago. Bromacil and simazine - two of the top roadside defoliators - have also been found in water samples.
 Chemicals that readily leach into groundwater are also very likely to run off compacted soil surfaces such as roadside shoulders. Diuron and simazine are among the toxic herbicides most frequently found in surface waters in the San Joaquin River watershed. In spite of this known propensity for these herbicides to pollute surface waters, there has been little, if any testing for herbicide runoff from California's roadsides.
Florida - which has analyzed and sampled chemicals that are suspected to contaminate surface runoff - found that some of the favorite roadside chemicals that are considered not to percolate to groundwater - such as glyphosate and oryzalin - are actually very likely to wash away with rainwater and then pollute surface waters. California, however, neither samples nor tests roadside surface water runoff for glyphosate, oryzalin or any of the herbicides sprayed along public roads.
Air
Even though roadside herbicides are known to drift and evaporate to pollute the air, Caltrans chose not to consider inhalation exposures at all when it conducted a 1992 assessment of the risk posed by its use of roadside chemicals. Inhalation of herbicides used on public roads is the most likely pathway of exposure to minions of travelers and those who work on roads, but neither Caltrans nor any other agency can accurately appraise the level of risk.
Recently there has been an increased focus on studying drift from agricultural spraying; herbicide drift has caused expensive losses to susceptible crops. But drift from roadside weed control has not been studied even though millions of people use sprayed roads and Caltrans uses application methods and chemicals known to cause drift. 14% to 78 % of glyphosate has been found to drift away from the sprayed target, and glyphosate residues have been detected up to 1,300 feet from where it was applied.
Statistically, the chance that a person can be exposed to a harmful, low-level dose of pesticides increases in proportion to the amount of chemical released into the environment at any one time. Also acting as factors are weather conditions, the expertise of the applicator, the age and worthiness of the application equipment and the types of chemicals applied. Such a welter of confounding factors makes being near herbicide applications a risky business, particularly in areas such as our public roads, which are frequented by millions of people.
Despite high public concern about air pollution, the Department of Pesticide Regulation (DPR) has been especially slow to identify which herbicides are the most hazardous air polluters. State laws passed in 1983 and 1984 established how DPR is to identify the pollution level and determine what needs to be done to reduce that pollution, but the agency's progress in upholding these laws has been painfully slow.
This chart indicates which of the top roadside chemicals were listed by DPR in 1994 as potential air toxins and describes the priority for testing each was given. There is no plan to test inert ingredients of pesticide formulations or herbicide breakdown-products - although these chemicals often pollute air as much as or more than the active ingredients.
Soil
Herbicides persist in soil; how much and for how long is determined largely by the chemical composition of the herbicide. Other variables also affect how long some chemical remains intact in soil, such as the number and type of soil organisms, level of organic matter, soil porosity, temperature, rainfall, acidity and many other factors.
As shown in this chart, of the top eight herbicides used for roadside vegetation control, half are highly persistent and the others are moderately long-lasting, depending on conditions. The pathway of exposure most likely to occur when these chemicals cling to soil particles is when dust from defoliated roadsides is disturbed by traffic or during construction, as has been shown when agricultural soils are disturbed. Who hasn't seen clouds of dust coming off summertime road construction projects?
Yet neither Caltrans nor any other agency has studied what effect repeated spraying of the same persistent herbicides to the same roadside soil has on the pollution level of dust buffeted around on its roads.
Though not well understood, how herbicides behave in the environment is the critical determinant of their impacts. Since enough is known to show that the herbicides used on roadsides have a great potential to pollute the environment and cause harm, and because there are non toxic options to their use, public road agencies should reduce and eliminate their use of these toxic chemicals.
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