Rate coefficients of hydroxyl radical reactions with pesticide molecules and related compounds: A review

• The ∙OH rate coefficients with aromatic pesticides are (2–10)×109 mol−1 dm3 s−1.
• For triazine type pesticides the values are around 2.5×109 mol−1 dm3 s−1.
• For non-aromatics with double bond or several C–H they are ~1×109 mol−1 dm3 s−1.
• For aromatics kOH’s are determined by diffusion; for triazines by chemical activation.
• They are activation controlled when molecule does not have double or C–H bonds.

Rate coefficients published in the literature on hydroxyl radical reactions with pesticides and related compounds are discussed together with the experimental methods and the basic reaction mechanisms. Recommendations are made for the most probable values. Most of the molecules whose rate coefficients are discussed have aromatic ring: their rate coefficients are in the range of 2×109–1×1010 mol–1 dm3 s–1. The rate coefficients show some variation with the electron withdrawing–donating nature of the substituent on the ring. The rate coefficients for triazine pesticides (simazine, atrazine, prometon) are all around 2.5×109 mol–1 dm3 s–1. The values do not show variation with the substituent on the s-triazine ring. The rate coefficients for the non-aromatic molecules which have C=C double bonds or several C–H bonds may also be above 1×109 mol–1 dm3 s–1. However, the values for molecules without C=C double bonds or several C–H bonds are in the 1×107–1×109 mol–1 dm3 s–1 range.