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.     

Impact of pasture contamination by copper,chromium, and arsenic timber preservative on soil microbial properties and nematodes

Microbial properties and nematode abundance were measured along a gradient of increasing Cu, Cr, and As concentrations (50–1300 mg Cr kg^-1) in the top 5 cm of a pasture soil contaminated by runoff of preserving liquor from an adjacent timber-treatment plant. Microbial biomass C and N were significantly (P<0.05) lower in contaminated than uncontaminated soils. The amount of microbial biomass C as a percentage of total organic C declined significantly (r ² value with Cr 0.726^*) with increasing contamination, and the ratio of respired C to biomass C was significantly (P<0.05) higher with contamination. Substrate-induced respiration, microbial biomass P, and denitrification declined (r² value with Cr 0.601, 0.833^*, and 0.709^*, respectively) with increasing contamination. Increasing contamination had no effect on prokaryote substrate-induced respiration but eukaryote: eukaryote substrate-induced respiration declined significantly (r ² value with Cr 0.722^*). Accordingly, the ratio of prokaryote substrate-induced respiration increased significantly (r ² value with Cr 0.799^*) with contamination. There was a significant (r ² value with Cr 0.872^*) hyperbolic relationship between sulphatase activity and contamination, with activity declining by approximately 80% at >1000 mg Cr kg^-1. Increasing contamination had no effect on basal respiration, dimethyl sulphoxide reduction, and phosphatase, urease, and invertase activities. Numbers of plant-associated nematodes declined significantly (r ² value with Cr 0.780^*) with contamination. On a percentage basis, plant-feeding nematodes predominated in less contaminated soils, whereas bacterial-feeding and predatory nematodes predominated in heavily contaminated soils. The use of the fumigation—incubation procedure for measurement of microbial biomass C in heavy-metal contaminated soils is discussed.     

Fluctuations in microbial biomass indices at different sampling times in soils from tussock grasslands

Microbial biomass in four topsoils from New Zealand tussock grasslands was estimated by three biochemical procedures at five sampling times over a 15 month period. In Conroy, Cluden and Tima soils, biomass C content was high in two sets of March (summer-autumn) samples and low in October (early spring) samples; in Carrick soil from a wetter, cooler environment, it was similar at all sampling times. Significant time-of-sampling variations occurred with Min-N flush in Tima and Carrick soils, and with adenosine 5'-triphosphate (ATP) content in three of the soils. Generally, the ratios of these biomass indices also varied significantly at some sampling times. Because of this variability, common factors could not validly be used with these soils for estimating biomass C contents from Min-flush or ATP values.The contribution of bacteria and fungi to the respiratory activity of the microbial biomass was unsuccessfully investigated using streptomycin and actidione as differential inhibitors of anabolic metabolism in the presence of added glucose. In three of the soils, rates of O₂ uptake did not generally increase significantly during incubation, even with added N, P, K and S or prior incubation overnight. In Conroy soil, rates did increase significantly, but the effects of the antibiotics separately and together could not be satisfactorily balanced.     

Soil translocation by weeding on steep-slope swidden fields in northern Vietnam

This study investigated soil translocation associated with weeding on steeply sloped swidden fields attended by ethnic Da Bac Tay farmers in Hoa Binh Province in northern Vietnam. Annual soil loss rates of 4–6 Mg ha⁻¹ year⁻¹ were found on 20 m plots located on two separate hillslopes. Median soil flux rates were equivalent to 2.6–3.9 kg m⁻¹ pass⁻¹ for experiments conducted on slopes ranging from 0.54 to 0.84 m m⁻¹. The primary soil translocation process, the mechanical movement of soil via contact with a small hoe (ngheo), contributed approximately 60% of the weeding-related soil flux. Ravel, which is the rolling, bouncing, and sliding of soil clods downslope, was a secondary translocation process that accounted for almost 40% of the soil flux. Soil flux was most appropriately described with an exponential function that could predict the occurrence of ravel on steeper slopes. The observed soil fluxes were much smaller than those determined during weeding and hoeing at other tropical and subtropical sites, primarily because the tillage depth was very shallow (<1 cm) and weed density was low at the time of experimentation. The erosion rates associated with weeding were an order of magnitude lower than reported water erosion rates; therefore, the contribution to landscape change was believed to be small. Combined water and tillage erosion estimates indicated a possible unsustainable increase in soil loss on some steep-slope fields within the last few decades that has resulted from shorter fallow periods, longer periods of cultivation before fallowing, and greater weed pressure. Additional work is needed to verify these latter interpretations.     

The effect of subsoiling and irrigation on potato production

Thin tillage pans restrict water movement and potato (Solanum tuberosum L.) root penetration in fine-textured soils of the Columbia Basin in central Washington State, U.S.A. Deep chiseling beneath potato rows, with simultaneous deep incorporation of fertilizer, was used to break-up the pans, enabling deeper root development. The effects of subsoiling on soil physical conditions and on potato production were examined under varying rates of irrigation. Deep tillage decreased soil strengths and bulk densities and increased porosity to depths of 10–16 cm below the pans. These improved subsoil physical conditions resulted in deeper root penetration, but the additional rooting only amounted to a small increase to the total root system. Cubic polynomial regressions demonstrated that subsoiling significantly increased potato yields under very droughty conditions but had no significant effects at intermediate (near optimum) levels of water application. Potato quality (percentage of U.S. No. 1 grade tubers and tuber specific gravity) was generally unaffected by deep tillage. These results indicate that, for potatoes, appropriate irrigation management can be used to overcome problems of restricted root penetration and impeded water movement caused by tillage pans.