Volatilization of 1,2‐dibromo‐3‐chloropropane (DBCP) from soils

Abstract

The volatilization of DBCP from soils, as affected by the soil characteristics and application techniques, was studied in a laboratory experiment. The volatilization rate of DBCP applied in water was higher from sandy and silty loam soils than from clay soil. Water added after DBCP application acted as a soil cover, decreasing the volatilization rate. The results obtained with DBCP application in hexane to air‐dry soils, indicate that adsorption could be an important factor in reducing the volatilization losses.

Diffusion coefficients were calculated from the volatilization parameters, by using a simplified relationship between volatilization losses and diffusion through soil.     

Nematicidal activity of terpenoids

Thirty four phytoterpenoids were evaluated for their nematicidal effect using the model nematode Caenorhabditis elegans. Nematicidal activities of the tested compounds at concentrations of 50 μg/mL showed wide variation in their effects ranging from no effect, weak, moderate and strong effects. Terpenoids exerting 50% or higher mortality at 50 μg/mL were further tested at five different concentrations to calculate the concentration that will kill 50% of the nematode population (LC₅₀). Among the most effective terpenoids were carvacrol, thymol, nerolidol, α-terpinene, geraniol, citronellol, farnesol, limonene, pseudoionone and eugenol in a descending order. These compounds exhibited a dose-dependent effect. The results suggest that the selected monoterpenoids and essential oils with a high concentration of these compounds mayprovide potential natural nematicides and merit further study as botanical nematicides for the control of both plant and animal parasitic nematodes. In general, oxygenated terpenoids and phenolic terpenoids exhibited higher nematicidal activity than hydrocarbons terpenoids.     

Natural organic compounds as alternative to methyl bromide for nematodes control

Thirty-three organic acids and furfural metabolites were examined for their nematicidal activity against plant-parasitic, free-living and predacious nematodes. Propionic acid, 2-methylhexanoic acid, lactic acid, maleic acid, and furic acid were the most effective nematicides among normal chain organic acids, branched organic acids, hydroxy/keto-acids, dicarboxylic acids and furfural metabolites, respectively. Seven of the tested compounds were found to have more than 90% mortality thus designating them as highly active nematicides. Of the highly active tested compounds, an average octanol/water log P of 0.97 was observed with a range from 0.28 to 2.64, and a Henry's Law constant averaging 2.6 × 10^{? 7} atm.m³/mole. Tested chemicals with minor or low nematicidal activity showed an average log P of 1.76 with a range from 0.15 to 3.42 and a Henry's Law constant averaging 16.6 × 10^{? 7} atm.m³/mole.