Stability of pesticides on solid-phase extraction disks after incubation at various temperatures and for various time intervals: interlaboratory study.

An interlaboratory study was conducted at 8 locations to assess the stability of pesticides on solid-phase extraction (SPE) disks after incubation at various temperatures and for various time intervals. Deionized water fortified with selected pesticides was extracted by using 2 types of SPE filtration disks (Empore C18 and Speedisk C18XF), and after extraction, the disks were incubated at 3 temperatures (25, 40, and 55 degrees C) and for 2 time intervals (4 and 14 days). Deionized water was fortified with atrazine, carbofuran, and chlorpyrifos by all participating laboratories. In addition, some of the laboratories included 2 of the following pesticides: metolachlor, metribuzin, simazine, chlorothalonil, and malathion. Concurrently, fortified water samples were extracted with the incubated samples by using each disk type at 4 and 14 days. Pesticides had equivalent or greater stability on > or = 1 of the C18 disk types, compared with storage in water. The lowest recoveries of carbofuran (6%) and chlorpyrifos (7%) were obtained at 55 degrees C after storage for 14 days in incubated water. At 55 degrees C after 14 days, the lowest recovery for atrazine was 65% obtained by using Empore disks. Pesticide-specific losses occurred on the C18 disks in this study, underlining the importance of temperature and time interval when water is extracted at remote field locations and the SPE disks containing the extracted pesticides are transported or shipped to a laboratory for elution and analysis.

Pesticide extraction efficiency of two solid phase disk types after shipping.

An interlaboratory study was conducted to compare pesticide recovery from Empore C(18) and Speedisks C(18)XF solid phase extraction disks after shipping. Four pesticides were used for the comparison of the two disk extraction materials: atrazine, diazinon, metolachlor, and tebuconazole. These pesticides were chosen to provide a range of physiochemical properties. Water samples were extracted onto the disk types and shipped to a cooperating laboratory for elution and analysis. The mean recoveries from Empore disks were atrazine, 95%; diazinon, 91%; metolachlor, 92%; and tebuconazole, 83%. The recoveries from Speedisks C(18)XF were atrazine, 89%; diazinon, 87%; metolachlor, 86%; and tebuconazole, 79%. Means for each of the pesticides using the different disk types were not statistically different (alpha = 0.05), but results were more variable when using Speedisks C(18)XF as compared to Empore disks. Reasons for the increased variability are discussed, but overall results indicate that Speedisks C(18)XF could be used as an alternative to Empore disks. Speedisks C(18)XF are enclosed in a plastic housing, so they can be used more easily in remote sampling sites without the possibility of glassware breakage, no prefiltration of samples is needed, and there are realignment problems that can be associated with the Empore disks.

Degradation of metolachlor in bare and vegetated soils and in simulated water-sediment systems.

A study was conducted to determine the half-life (t1/2), degradation rate, and metabolites of metolachlor in a water-sediment system and in soil with and without switchgrass. Metolachlor degradation in a laboratory was determined in sediment from Bojac sandy loam soil incubated at 24 degrees C. The study also was conducted in a greenhouse on tilted beds filled with Bojac soil and planted with switchgrass. In both experiments, samples were collected at days 0, 7, 14, 28, 42, 56, and 112 and analyzed for metolachlor and its major metabolites. The water-sediment oxidation-reduction potential took 28 d to reach -371 mV and the pH increased from 5.6 to 6.5 by the last sampling day (day 112). The average soil temperature of the tilted beds with or without switchgrass during the study was 21degrees C and the soil moisture content was 23% by volume. The t1/2 of metolachlor was 34 d in sediment and 8 d in the water phase. The t1/2 of metolachlor in soil from the switchgrass filter strip (6 d) was not different from that in soil without grass (9.6 d). The metolachlor metabolites ethanesulfonic acid (ESA) and oxanilic acid (OA) were detected in the water-sediment system and in soil from tilted beds. In both sediment and soil from tilted beds, the two metabolites peaked by day 56 of incubation and declined after that, indicating transformation to other products. In the water-sediment system, greater quantities of OA and ESA were detected in sediment than in the aqueous phase. The production of OA and ESA in the watersediment system occurred in the first 28 d, when the system was at an aerobic redox state. Metolachlor can degrade in sediment and the relatively high soil temperature and moisture level accelerated its breakdown in beds with and without switchgrass. Under warm and moist soil conditions, the presence of switchgrass has no effect on the degradation of metolachlor.

Interlaboratory comparison of extraction efficiency of pesticides from surface and laboratory water using solid-phase extraction disks.

A continuation of an earlier interlaboratory comparison was conducted (1) to assess solid-phase extraction (SPE) using Empore disks to extract atrazine, bromacil, metolachlor, and chlorpyrifos from various water sources accompanied by different sample shipping and quantitative techniques and (2) to compare quantitative results of individual laboratories with results of one common laboratory. Three replicates of a composite surface water (SW) sample were fortified with the analytes along with three replicates of deionized water (DW). A nonfortified DW sample and a nonfortified SW sample were also extracted. All samples were extracted using Empore C(18) disks. After extraction, part of the samples were eluted and analyzed in-house. Duplicate samples were evaporated in a 2-mL vial, shipped dry to a central laboratory (SDC), redissolved, and analyzed. Overall, samples analyzed in-house had higher recoveries than SDC samples. Laboratory x analysis type and laboratory x water source interactions were significant for all four compounds. Seven laboratories participated in this interlaboratory comparison program. No differences in atrazine recoveries were observed from in-house samples analyzed by laboratories A, B, D, and G compared with the recovery of SDC samples. In-house atrazine recoveries from laboratories C and F were higher when compared with recovery from SDC samples. However, laboratory E had lower recoveries from in-house samples compared with SDC samples. For each laboratory, lower recoveries were observed for chlorpyrifos from the SDC samples compared with samples analyzed in-house. Bromacil recovery was <65% at two of the seven laboratories in the study. Bromacil recoveries for the remaining laboratories were >75%. Three laboratories showed no differences in metolachlor recovery; two laboratories had higher recoveries for samples analyzed in-house, and two other laboratories showed higher metolachlor recovery for SDC samples. Laboratory G had a higher recovery in SW for all four compounds compared with DW. Other laboratories that had significant differences in pesticide recovery between the two water sources showed higher recovery in DW than in the SW regardless of the compound. In comparison to earlier work, recovery of these compounds using SPE disks as a temporary storage matrix may be more effective than shipping dried samples in a vial. Problems with analytes such as chlorpyrifos are unavoidable, and it should not be assumed that an extraction procedure using SPE disks will be adequate for all compounds and transferrable across all chromatographic conditions.

Interlaboratory comparison of pesticide recovery from water using solid-phase extraction disks and gas chromatography.

An interlaboratory study was conducted to assess the suitability of C18 solid-phase extraction disks to retain and ship different pesticides from water samples. Surface and deionized water samples were fortified with various pesticides and extracted using C18 disks. Pesticides were eluted from disks and analyzed in-house, or disks were sent to another laboratory where they were eluted and analyzed. Along with the disks, a standard pesticide solution in methanol was also shipped to be used for fortification, extraction, and analysis. The highest recovery from deionized or surface water using shipped disks was obtained for cyanazine (>97%), followed by metalaxyl (>96%), and atrazine (>92%). Although <40% of the bifenthrin, chlorpyrifos, and chlorothalonil fortified in surface water was recovered from shipped disks, recoveries from deionized water were >70%. From in-house eluted disks, bifenthrin and chlorpyrifos were recovered at 118 and 105%, whereas chlorothalonil showed 71% recovery, indicating that poor recovery from surface water was due to loss during shipping rather than low retention by the C18 disks. There was no consistent relationship between recovery from C18 disk and physicochemical properties for the pesticides included in this study. For most of the 13 pesticides tested, there were no differences in recovery between in-house extracted disks and shipped disks, indicating the suitability of disks to concentrate and transport pesticides extracted from water samples.