Tolerances for pesticides are typically expressed in which unit?

Tolerances for pesticides are commonly expressed in parts per million (ppm). This unit measures the concentration of a substance in relation to a million parts of the total. In the context of pesticides, it indicates the maximum permissible level of pesticide residues that may be present on foods or in the environment. The use of ppm is particularly advantageous as it allows for easy comparison and scaling of pesticide concentrations, regardless of the total quantity being assessed.

While mg/kg is also a valid unit that can express concentrations similar to ppm (since 1 ppm is equivalent to 1 mg/kg in terms of weight), the standard industry practice typically favors the ppm designation for clarity and uniformity in regulatory contexts. Other units such as lbs/A (pounds per acre) and oz/acre are more relevant for measuring the application rates of pesticides rather than the tolerances or permissible residue limits. Thus, ppm is the most appropriate answer when discussing how tolerances for pesticides are expressed.