The safety of a dose of anything depends heavily on at least two things -- the susceptibility of the organisms that are being dosed and the strength of the material that is being distributed. It is not necessarily the case that a small enough dose of any given material is harmless. For example, for some materials such as plutonium, there is no known safe dose for humans -- one atom might be enough to induce cancer. Dioxin is yet another chemical group that has some effect at any measurable dosage.
The SYMVCD indicates that it is distributing 2/3 oz. of Evergreen 60-6 per acre, which over roughly 10 square miles of Davis and Woodland yields roughly 4,267 oz., a significant amount of poison. To compare relative exposures; a 12 oz can of household ant and roach killer contains 0.68 gm active pyrethroid ingredient. Each night's spray activity over Sacramento in 2005 thus released the equivalent of 1.5 million 12 oz cans of household spray [55,000 acres covered, 0.66oz/acre, 28.5gm/oz, and 0.68gm/12 oz can = 1,521,397 12 oz cans].
Since the size of the dose does not guarantee safety in general, it is very important to have an excellent understanding of both the short-term and long-term effects of any chemical SYMVCD is distributing into the environment. Indeed, this amount of the nerve gas sarin, an organophosphate, would likely result in many human mortalities and significant lethality to all animals.
Pyrethrums are considered to be less dangerous than the organophosphates, but what are the effects of the distribution of this amount of Evergreen 60-6, pyrethrum synergized with piperonyl butoxide (PBO) and mixed with unknown other materials, called "inert?" See our discussion of the risks of these chemicals, including major concerns over the so-called "inert" ingredients. How many of our daughters are we setting up for breast cancer while purportedly saving them from West Nile virus? How many of our citizens are at risk for serious allergic reactions or worse?
Vector Control officials and their apologists speak of the response of healthy individuals to being sprayed with Evergreen 60-6 and completely ignore the special susceptibilities of at-risk groups in the population. Both pyrethrum and PBO are toxic to a wide range of organisms to differing degrees. Both poisons are toxic to healthy people at the dosage of between 750 mg to 1 gram per kilogram. But the liver toxicity and neurotoxicity of pyrethrum as well as the liver toxicity of PBO are significantly greater in persons with liver disease, since the enzymes from the liver are what detoxify the poison in healthy persons. All infants under six months of age are more acutely susceptible since they do not produce the full complement of liver enzymes. Effects that are delineated as sub-acute in healthy persons will be potentially fatal to those suffering from neurological diseases such as Parkinson’s disease or MS. Those who suffer asthma or COPD (Chronic Obstructive Pulmonary Disease, or emphysema) will be seriously at risk to the inhalation exposure, and for this specific reason many areas of the country, such as Washington DC and Bethesda (around the NIH), opted not to spray at all out of concern for those suffering from asthma. The “inert” ingredients are equally a concern for asthmatics.
Recent research demonstrated that PBO got into the sediment of the waterways around Sacramento and synergized toxic chemicals that were already present, making them twice as toxic in some cases. One obvious question is what other toxic chemicals in our environment might PBO be synergizing, even in our bodies.
The widespread broadcast of low concentrations of materials in this fashion is the recipe for creating resistance in non-target insects. Fleas, as nest parasites and the vectors of bubonic plague, are most commonly present in lawns and turfs frequented by dogs and cats. The larval stage is always in the nest, while the blood-feeding adults hop on and off the host for feeding. They most certainly will become exposed to a widespread broadcast of insecticides from the air. Plague is chronically present in rodent populations in some areas of California such as Lassen County and even Golden Gate Park. If resistance is induced in the flea populations, there will be no effective control available when antibiotic-resistant plague encroaches upon the California ecosystem. We will then truly understand what a major urban epidemic of insect-vectored disease is really like!
Spraying low doses of some materials can make mosquitoes more aggressive biters and make the problem worse. An example is the cholinesterase inhibitors.
“The dose makes the poison,” so the argument goes, and then the implication often is that the chemical in question is being applied in such a small dose that there could be no possible harmful effect. This comes from the so-called “dose-response relationship,” which has governed pesticide regulation for years. The old theory is that any substance is harmless if applied at levels below a certain amount, a response then occurs as the amount is increased past that point, the response increases as the dose is increased, and the response eventually levels off after a point. However, this is out-of-date, and pesticide regulation has not kept pace but is slowly being revised. As noted above, there are situations in which no minimal level of dose has been found that does not generate a response, and there are also situations with inverted dose-response relationships -- increased responses at decreased doses. See the ABCs of Toxicology for further details.
Along these lines, Beyond Pesticides recently indicated that "A new study showing that the order of exposure to multiple pesticides may be just as important as the dose, timing and length of exposure adds another dimension to the complex task of risk assessments," and that "For the first time, the World Health Organization (WHO) released a report in July on children’s heightened vulnerability to chemical exposures at different periods of their growth and development. The organization cites over 30% of the global burden of disease in children can be attributed to environmental factors, including pesticides."
In the past people understood chemicals such as arsenic weren’t safe and they didn’t put them in waterways or fountains from which people might drink. It’s only the “modern” insecticides starting with DDT where pharmacodynamic models lured people into delusions of safety. DDT was banned because of bioaccumulation and environmental concerns, then DDVP (dichloro divinyl organophosphate) was banned for carcenogenicity, and then Dursban (chlorpyrifos) was restricted for hazards to children. Might pyrethrum and/or PBO be next? The long-term effects of these chemicals have not been adequately studied, but experience shows that we cannot automatically assume that they are safe at “low” doses.