Pesticide Impact Calculator

This tool combines two independent ideas about pesticide risk. The first is hazard scoring. Acute mammalian toxicity is summarised by the LD50, the single dose in milligrams per kilogram of body weight that kills half a test population, where smaller numbers mean greater toxicity; parathion sits near 13 mg/kg while glyphosate is often quoted above 4,000 mg/kg. The WHO hazard classes used here follow that scale, with class Ia below 5, Ib below 50, class II to 2,000 and class III above it. Persistence is scored from the soil half-life, conventionally treating under 14 days as non-persistent, 14 to 60 days as moderately persistent and beyond 60 days as persistent. Combining a toxicity score and a persistence score into a base index, then multiplying by application rate and number of applications per season, follows the logic of the field use Environmental Impact Quotient: the same chemical applied twice as often imposes twice the loading. The second idea is degradation kinetics. Residues are assumed to decline by first-order decay, so the concentration remaining after time t is the initial amount times e to the power of minus kt, where k equals the natural log of 2 divided by the half-life. That algebra means 90 percent has degraded after about 3.3 half-lives and 99 percent after about 6.6, which is the basis for setting pre-harvest intervals. Several limits deserve emphasis. The index here is a simplified analogue of the published EIQ and will not reproduce Cornell EIQ values. LD50 measures acute rodent toxicity only and says nothing about chronic effects, endocrine activity, or toxicity to bees, earthworms and fish, which is where many field problems actually arise. Real field dissipation is often biphasic rather than cleanly first-order, and half-life varies severalfold with soil pH, organic matter, temperature and moisture.

Quantitative toxicology gave this field its base unit when John William Trevan, working at the Wellcome Physiological Research Laboratories, introduced the LD50 in a 1927 paper, arguing that a median lethal dose was statistically more stable than trying to identify a minimum lethal dose. Dose-response analysis was put on firmer footing by Chester Bliss with the probit method in the 1930s. Regulatory concern about ecological and residue effects intensified after Rachel Carson published Silent Spring in 1962; the United States Environmental Protection Agency was created in 1970 and banned most DDT uses in 1972, and the World Health Organization issued its Recommended Classification of Pesticides by Hazard in 1975, keyed to LD50 bands and revised periodically since. Comparing whole spray programmes rather than individual chemicals required a composite index. In 1992 Joseph Kovach, Charles Petzoldt, James Degni and James Tette of the New York State Integrated Pest Management Program at Cornell University published the Environmental Impact Quotient, which averages a farmworker component, a consumer component and an ecological component covering fish, birds, bees and beneficial arthropods, then scales the result by rate and frequency to give a field use EIQ. The measure was adopted widely in extension work and IPM programme evaluation, and also criticised, notably in a 2015 PLoS ONE analysis by Andrew Kniss and Carl Coburn, for weighting hazard without accounting for exposure. Alternative indices such as the Danish Pesticide Load Indicator and the Pesticide Risk Hazard Index were developed in response.