A farmer is applying glyphosate (C3H&NO5P) to an agricultural field, and the top
ID: 145316 • Letter: A
Question
A farmer is applying glyphosate (C3H&NO5P) to an agricultural field, and the topsoil in the field is in equilibrium with runoff water that eventually comes in contact with a sensitive endangered plant population. Assume the maximum safe concentration of glyphosate that can be present in the runoff water is 0.70 mg/L, and the fraction of organic carbon in the topsoil is 0.05. (a) (10 pts) The Koc for glyphosate is 2100 L/kg (from EPA's Chemistry Dashboard (https://comptox.epa.gov/dashboard/)). If the topsoil is in equilibrium with runoff water containing the maximum safe concentration of glyphosate, what is the mass/mass concentration, q (mg/kg), of glyphosate in the topsoil? (b) (10 pts) Assume a 1-acre field has 200,000 kg of topsoil in equilibrium with 50,000 L of runoff water during a rain event. What is the maximum total mass (in water and soil combined) of glyphosate (in kg) that could be applied to this field and stay within the limit on the runoff water concentration?Explanation / Answer
The farmer is applying the glyphosate to an agricultural field, and the maximum safe concentration of glyphosate present in runoff water is 0.70mg/L.
The fraction of organic carbon in the topsoil is 0.05.
The given question was if 1 acre field has 200, 000 kg of top soil in equilibrium with 50,000L of runoff water, then the amount of glyphosate in kg is?
The 200,000kg of soil contains 0.14kg of glyphosate.
And the 50,000L contains 0.035kg of glyphosate.
Both water and soil contains 0.175kg of glyphosate.
Hence 1 acre field should be applied with 0.175kg of glyphosate within the limit on the runoff water concentration.
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