S. Baskaran

Degradation of bifenthrin, chlorpyrifos and imidacloprid in soil and bedding materials at termiticidal application rates

Organophosphorus, pyrethroid and chloronicotinyl insecticides have been used to control termites in building structures in recent years. We investigated the degradation behaviour of three insecticides (bifenthrin, chlorpyrifos and imidacloprid) at termiticidal application rates under standard laboratory conditions (25 °C, 60% field moisture capacity and darkness) for 24 months. The study was carried out on one soil and two bedding materials (sand-dolomite and quarry sand), which are commonly used under housing in Australia. Experiments were also conducted to examine the effect of soil moisture on the degradation of these insecticides. Insecticide residues in the samples collected at different days after application were measured by high performance liquid chromatography (HPLC). The rate of degradation of bifenthrin and imidacloprid insecticides was adequately described by a first-order kinetic model (r2 = 0.93–0.97). However, chlorpyrifos degradation was biphasic, showing an initial faster degradation followed by a slower rate. Therefore, the degradation data during the slower phase only (after a two-month period) followed the first-order law (r2 = 0.95). Soil moisture had little effect on degradation of imidacloprid and bifenthrin. Among the three insecticides, bifenthrin and imidacloprid were most stable and chlorpyrifos the least. Chlorpyrifos showed a major loss (75–90%) of residue during the 24 months incubation period. In the bedding materials, simultaneous accumulation of the primary metabolite of chlorpyrifos, TCP (3,5,6-trichloro-2-pyridinol) was observed. Hydrolysis appeared to have caused the observed rapid loss of chlorpyrifos, especially in the highly alkaline bedding materials (sand-dolomite and quarry sand). © 1999 Society of Chemical Industry

Determination of the insecticide imidacloprid in water and soil using high-performance liquid chromatography

We describe an analytical technique for measuring residues of imidacloprid, a relatively new and highly active insecticide, in water and soil using high-performance liquid chromatography (HPLC). All analyses were performed on reversed-phase HPLC with UV detection at 270 nm using a mobile phase of acetonitrile-water (20:80, v/v). Fortified water samples were extracted with either solid-phase extraction (SPE) or liquid-liquid extraction methods. A detection limit of 0.5 microgram/l was achieved using the SPE method. The imidacloprid residues in soils were extracted with acetonitrile-water (80:20, v/v), and the extract was then evaporated using a rotary evaporator. The concentrated extract was redissolved in 1 ml of acetonitrile-water (20:80, v/v) prior to analysis by reversed-phase HPLC. A detection limit of 5 micrograms/kg was obtained by this method which is suitable for analysis of environmental samples. Accuracy and precision at 10 and 25 micrograms/kg soil samples were 85 +/- 6% and 82 +/- 4%, respectively.

An evaluation of the methods of measurement of dissolved organic carbon in soils, manures, sludges, and stream water

Abstract Dissolved organic carbon (DOC) from various organic matter sources was measured using spectrophotometric, wet oxidation, and dry combustion methods. The relationship between light absorption at 250 nm and the concentration of DOC varied between the sources which is attributed to the difference in the nature of organic compound, as measured by the relative molecular weight fractions in the DOC samples. Wet oxidation achieved only a partial oxidation of the DOC and the extent of oxidation varied between the sources. Dry combustion achieved the complete recovery of DOC. Both air drying and oven drying increased the concentration of DOC; whereas freeze drying had no effect on the concentration of DOC. DOC concentration increased with an increase in pH.

Non-Equilibrium Sorption during the Movement of Pesticides in Soils

Sorption and movement of two ionic herbicides (2,4-D and atrazine) and two non-ionic insecticides (phorate and terbufos) in an allophanic (Patua silt loam) and a non-allophanic (Tokomaru silt loam) soil were examined using 14C- labelled pesticides. For sorption measurements, a range of concentrations of pesticide solutions in 0.1 M calcium chloride were shaken with soil samples at a soil: solution ratio of 1 : 10 for 4 h at 25°C. The movement of pesticides was examined using re-packed soil columns following a step input of 2,4-D and tri- tiated water (3HzO) and a pulse input of 2,4-D, atrazine, phorate and terbufos. A convection-dispersion equation (CDE), either with an equilibrium or a bicon- tinuum non-equilibrium sorption process, was used to simulate the measured effluent breakthrough curves (BTCs) obtained by simultaneous displacement of a non-sorbed solute (3H20) and a sorbed solute (2,4-D). The Patua soil sorbed more pesticide than did the Tokomaru soil. This is attributed to the larger amounts of organic matter and the presence of short- range order clays (allophane) in the former soil compared to the latter. Kinetic sorption data for pesticides showed an initial rapid rate followed by a slower rate of sorption. In column experiments, the pesticide in the leachate appeared later in the Patua than in the Tokomaru soil. Movement of pesticides in soils decreased with an increase in K, values. The step-function experiments showed a symmetrical BTC for the non-sorbed solute (3HzO) with a sigmoidal shape, whereas there was an asymmetrical BTC with extensive tailing for the sorbed solute (2,4-D). The CDE with an equilibrium sorption process adequately described the 3H,0 BTC, but failed to simulate the BTC for 2,4-D. The CDE with a bicontinuum non-equilibrium sorption process provided a good descrip- tion of the BTC for 2,4-D. Diffusion of pesticides into sorbent organic matter was considered to be the likely mechanism for the observed sorption non- equilibrium during the movement of pesticides in soils.

High-performance liquid chromatographic determination of flumetsulam, a newly developed sulfonamide herbicide in soil

Abstract An analytical method is described for measuring residues of flumetsulam, [N-(2,6-difluorophenyl)-5-methyl-[1,2,4]triazolo[1,5-a]pyrimidine-2-sulfonamide] in soil using high-performance liquid chromatography (HPLC). The soil is extracted with aqueous NaHCO3, and the extract solution acidified then passed through a C18 solid-phase extraction (SPE) disc. The concentrated extract obtained is then cleaned up by gel permeation chromatography (GPC) on Bio-Beads SX-3 prior to analysis by reversed-phase HPLC with UV detection. A detection limit of 4 μg/kg is obtained by this method which is suitable for routine residue decay trials.