Alachlor with time

Figure 14. Alachlor degradation with time, a, amount in soil and water o, amount in water.

The use of solar powered systems for destruction of a mixture of pesticides in well water including dichloroaniline, benzopyran, atrazine, propazine, alachlor, prometryn, bromacil and cyanobenzoate has been achieved [124], Variable efficiencies for the decomposition of these compounds was observed with over 90% of dichloroaniline destroyed in 10 h compared to 50% of propazine in the same period. In general for most of the pesticides examined the half life time for the process in the 100 ppb concentration range was less than 1 h. 

In this procedure, the interferences are removed by SPE and the analytes pass through the sorbent. An example is the isolation of nonionic herbicides from soil, atrazine and alachlor. Because soil is commonly extracted with methanol or acetonitrile, there is a substantial amount of humic material extracted at the same time. Both methanol and acetonitrile are miscible with water and readily penetrate the pores and surfaces of soil organic matter, which is hydroscopic and contains sorbed water. Because soil organic matter is attached to silicate surfaces and iron and aluminum hydroxides, it readily binds water to its... 

The methanol extract of soil is diluted with water to increase the affinity of the solute for the C-18 sorbent. Figure 7.6 shows the effect of methanol concentration on the sorption capacity of atrazine and other triazine herbicides for C-18. At concentrations of methanol less than 10%, the capacity of the sorbent is more than adequate to isolate the atrazine and alachlor from the methanol/water phase. This procedure is many times simpler than evaporating the methanol however, methanol evaporation may be necessary if more water-soluble compounds are present. 

The dissipation of metolachlor in the soil is three times slower than that of alachlor. Gerber et al. (1974) found, at 22°C and a 50% soil moisture content in sandy loam of 3.8% organic content, a 50% dissipation time of 26 days. Under identical laboratory conditions this value was 60 days for atrazine, 100 days for trifluralin and 80 days for diuron. Under field conditions, metolachlor is completely degraded in a growing season, and thus does not interfere, with crop rotation. 

Hogenboom, C., Niessen, W. M. A., and Brinkman, U. A. Th., Characterization of photodegradation products of alachlor in water by online solid-phase extraction liquid chromatography combined with tandem mass spectrometry and orthogonal-acceleration time-of-flight mass spectrometry. Rapid Commun. Mass Spectrom., 14, 1914-1924, 2000. 

Table V. Action of 37 yuM alachlor on Chlamydomonas reinhardii growth and multiplication when present for different time-intervals during the growth cycle. Inoculation was with stationary algae with a cell volume of 90, um. Light phases were from 0-10, 24 - 3A and 48 - 58 h. C = Control, A = alachlor-treated.

In MAE, the sample is suspended in conventional extraction solvents (e.g., -hexane, methanol-water) and irradiated for 30 s in a kitchen-type microwave oven (frequency 2450 Hz) without allowing the suspension to boil. Irradiation steps are repeated several times to obtain the maximum yield of extracted compounds. After irradiation, the sample is centrifuged and the supernatant removed for analysis [112]. SPE-MAE has thus been used for the extraction of atrazine, alachlor, and a-cypermethrin from water samples with recoveries ranging from 93.3% to 105.3% [113]. 

Fig. 4.4 LC-TOF MS spectra and accurate measurements for the secondary amides of alachlor (a) and acetochlor (b) sulfonic acid in a groundwater sample. The correct elemental composition for both analytes ranks at the second score position. The physico-chemical properties and the chromatographic retention times were predicted from the molecular structure (Ferrer and Thurman 2003, Fig. 4.3, with permission)...

In the green alga Scenedesmus acutus the uptake of 2- C) acetate, a precursor of fatty acid synthesis, is inhibited with 100 pM alachlor and 100 pM metazachlor within an incubation time of 4 h (1). There is also shown that the incorporation of the labeled acetate in acyl lipids is inhibited. After 16 h and 40 h incubation with a herbicide concentration of 5 yM the fatty acid content of the green alga changed, as shown in the table. 

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