There are many challenges in developing a relative cumulative ranking system for the safety of pesticides at any scale and for any user group:
- Inherent uncertainties (unknown factors that are a property of observer and may be reduced by further research) in toxicological data, as it would be exceedingly costly and nearly impossible to conduct test of all possible non-target/target species that may be exposed to a pesticide. There are many examples of this, but for instance, the honey bee acts as a surrogate species for all non-target terrestrial insects in the EPA's current regulatory framework for ecological toxicity tests. However, there are many species of insects within the United States and there is likely species-to-species variability in susceptibility to pesticides that is unaccounted for in the data.
- Lack of availability of pesticide use data, especially at smaller spatial scales (i.e., county level). Pesticide sales data are available for pesticides for the entire United States, as reported by the registrants. One cannot truly calculate risk without accurate estimates of pesticide use. For South Carolina, the National Agricultural Statistics Service (NASS) has the best approximation of use that can be obtained (to the author's knowledge), and it is not broken down into specific pesticides (click asterisk for more information). These data are only for agricultural areas as well, which does not fully encompass all areas where pesticides are applied. The U.S. EPA estimates that approximately 75% of all pesticide usage in the United States is agricultural and the other 25% is for home, garden, industrial, commercial, and government applications.21 Sales data of pesticides are available to the public, but actual use (i.e., application) of products is proprietary with the exceptions being California and New York.*
- Determining thresholds for different parameters considered in the Pesticide Decision Making-Tool presents its own challenges. Here, we utilized EPA's system of hazard ranking for toxicity values, and professional judgment to establish thresholds for environmental fate parameters.
- There is also the issue of comparing human health risk characterization values (with safety factors) to ecological health values (without safety factors). These two measures of risk (i.e., %RfD, RQ) are not equal and therefore not directly comparable. With these challenges acknowledged, we proceeded to develop a cumulative ranking system with the best available data and using the most conservative (and therefore safest) estimates for all parameters considered within the Pesticide Decision Making-Tool. For mammalian data, we calculated RQs for the chronic risk and is only applicable to small mammals (e.g., squirrel) not necessarily humans.
- Only the active ingredient (AI) is tested during toxicological testing, but is usually found in a formulation with more than one AI, meaning it could alter the toxicity of an AI.
- An AI's byproducts (pesticide changes state as it enters into the environment or is absorbed, distributed, metabolized, and excreted by organisms. These byproducts may be more or less toxic than the original AI that is applied.
* South Carolina Farming and the Three County Target Region
The National Agricultural Statistics Service (NASS) conducted the 27th federal census of agriculture in 2007 (NASS 2011). As part of the census, an estimate of chemical usage on farmland is collected at the national, state, and county levels. When looking at this dataset it is important to remember that the estimates provided are approximations for farmland alone, therefore they are underestimates of actual usage because other use categories are not included. However, to the author's knowledge NASS’s chemical use estimates on farmland are the only estimates available to the public. In South Carolina, for the 2007 farming season, 34% of agricultural sales were crop sales (valued at $798 million) and 66% were livestock sales (valued at $1.5 billion) (NASS 2007). A total of 746,890 acres of farmland were treated with pesticides in the state of South Carolina (Table 1). Statewide herbicides were the pesticides most frequently used on farms, followed by insecticides. At the county level, herbicides were more frequently used in Jasper and Hampton Counties compared to Beaufort, where more insecticides were utilized in the 2007 estimates.
Farmland (# acres) treated with various pesticides for control of insect, weed, nematode, and disease pests in South Carolina (SC), and in the three target counties for the PDMT: Beaufort, Hampton, and Jasper Counties, SC.