Effect of Soil pH on Microbial Degradation, Adsorption, and Mobility of Metribuzin

Abstract

Metribuzin [4-amino-6-tert-butyl-3-(methylthio-as-triazin-5(4H)one] degradation by soil microorganisms decreased as the soil pH decreased. Metribuzin and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] mobility increased with increasing concentration and soil pH.14C-metribuzin had greater mobility on soil thin-layer plates than14C-atrazine because of differences in water solubility and basicity. Adsorption increased with decreasing soil pH. The pKa for metribuzin was 0.99 ± 0.08. Adsorption increased gradually as the soil pH decreased toward the pKa of metribuzin. Protonation of the amine group with subsequent adsorption to soil colloids was the postulated reason for the reduction in phytotoxicity, microbial degradation, and mobility of metribuzin at low soil pH levels.

Sugarcane and pinewood biochar effects on activity and aerobic soil dissipation of metribuzin and pendimethalin

“…The presence of the ash was inferred from the relatively high pH measured with the ash was mixed with water (Table 2). Increasing pH has been reported to decrease metribuzin adsorption by soil and increase degradation rates (Ladlie et al, 1976).…”

Extraction of Metribuzin from Soil Using Supercritical CO 2 (SFE)

“…This effect was even more dramatic at the 2% modifier addition where the mean recovery increased from 17.01% to 60.63% with the addition of triethylamine (results not reported in Table 2) Metribuzin has been reported to become protonated, thereby increasing adsorption as soil pH decreases (Ladlie et al 1976). The lower the soil pH the higher the degree of protonation.…”

“…The effect of pH was also beyond the scope of these triazine studies. Metribuzin adsorption to soil is especially sensitive to pH due to its protonation at low soil pH (Ladlie et al, 1976).…”

Benzene and toluene biodegradation down gradient of a zero-valent iron permeable reactive barrier

“…The main intermediate of benzene degradation is phenol, while benzoic acid is the main by-product of toluene degradation [36,37]. Ladlie et al [38] have postulated that the biodegradation rate of any given organic compound corresponds closely with its ionization constant (pK a ) and the matrix pH. The pK a of phenol at 25 • C is 10.0, while the pK a of benzoic acid is 4.2.…”