The California Department of Pesticide Regulation, using less-sensitive tests,
found that:1) 31 percent of conventionally grown samples had pesticide residues; 2)
6.5 percent of organic samples had pesticide residues; and 3) conventional samples
had multiple residues nine times as often as organic samples.
Consumers Union showed the following:1) 79 percent of conventionally grown
samples had pesticide residues; 2) 27 percent of organically grown samples had pesti-
cide residues; and 3) conventional samples had multiple kinds of residues ten times
as often as organic samples.
Not only did fewer organic samples have any pesticide residues, but the level of
pesticide residue found was consistently lower than the amounts found in conventional
foods. The authors believe that residues found in organic foods could have been in the
soil from previous pesticide use or could have come from pesticides sprayed on neigh-
boring farms.^18
The Reference Dose
How is pesticide safety determined for humans? The EPA establishes a reference
dose (RfD) for each pesticide it approves for use. The RfD is the amount of a chemi-
cal that, if ingested over a lifetime, is not expected to cause any adverse health effects
in any population subgroup. The RfD includes a ten- to 10,000-fold safety factor to
protect humans over a lifetime, including infants, children, and other special popula-
tions. Using food consumption patterns and other data, the EPA estimates how much
pesticide residue is likely to be consumed. If the RfD is exceeded the agency takes
steps to limit the use of the pesticide.
Dose Response
Ironically, the extensive amount of data developed about a pesticide is often used
against it by ignoring the dose response. For example, some acute toxicity studies,
which are designed to include dosage levels high enough to produce deaths, are cited
as proof of a chemical’s dangers. Chronic effects seen at very high does in lifetime
feeding studies are misinterpreted, according to the EPA, and considered as proof
that no exposure to the chemical should be allowed, even though major improve-
ments in analytical chemistry permit detection of the presence of chemicals at levels
of parts per billion (ppb) or even parts per trillion (ppt).
We may hear that a certain chemical has been found in a food or beverage, and
that the amount found is expressed in parts per million or parts per billion. Often,
no information is provided to assist us in comprehending the meaning of these num-
bers. Frequently, this information neglects the issue of dose response, the key princi-
ple of toxicology, which simply stated is ‘‘the dose makes the poison.’’ The
concentration of a chemical in any substance is meaningless unless it is related to the
toxicity of the chemical and the potential for exposure and absorption. Chemicals of
low toxicities, such as table salt or ethyl alcohol, can be fatal if consumed in large
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