calculations: the first-order rate law for the decay of pesticides is dP/dt = -kP where P is the amount of pesticide, t is the time and k is the rate constant for degradation. To calculate the amount of pesticide at any time after application the equation P(t) = P_o*Exp(-kt) is used where P_o is the original amount of pesticide. k can be calculate with the equation k = 0.693/hlife. decay_f or decay_s = Exp(-k)