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.     

Influence of Nitrogen Addition and Plant Root Parameters on Phytoremediation of Pyrene-contaminated Soil

Phytoremediation is a method in which plants, soil microorganisms, amendments, and agronomic techniques interact to enhance contaminant degradation. We hypothesized that bermudagrass (Cynodon dactylon L) and an appropriate amount of N fertilizer would improve remediation of pyrene-contaminated Captina silt loam soil. The soil was contaminated with 0 or 1,000 mg pyrene/kg of soil and amended with urea at pyrene-C:urea-N (C:N) ratios of 4.5:1, 9:1, 18:1, or unamended (36:1). Either zero, one, two, or three bermudagrass sprigs were planted per pot and ?33 kPa moisture potential was maintained. Pyrene concentrations, inorganic-N levels, shoot and root parameters, and pyrene degrader microbial numbers were measured following a 100-day greenhouse study. At a C:N ratio of 4.5:1, the presence of plants increased pyrene biodegradation from 31% for the no plant treatment to a mean of 62% for the one, two, and three plant treatments. With no plants and C:N ratios of 4.5:1, 9:1, 18:1, and 36:1, the mean pyrene biodegradation was 31, 52, 77, and 88%, respectively, indicating that increased inorganic-N concentration in the soil reduced pyrene degradation in the treatments without plants. Additionally, none of the one, two, or three plant treatments at any of the C:N ratios were different with a mean pyrene degradation value of 69% after 100 days. Pyrene resulted in reduced shoot and root biomass, root length, and root surface area, but increased root diameter. The pyrene degrading microbial numbers were approximately 10,000-fold higher in the pyrene-contaminated soil compared to the control. At the highest N rate, bermudagrass increased pyrene degradation compared to the no plant treatment, however, in the unvegetated treatment pyrene degradation was reduced with added N.     

Sediment-Water Interactions Affect Assessments of Metals Discharges at Electric Utilities

We present three examples to show the importance of sediment-water interactions to electric utilities: 1) Selenium (Se), in ash pond effluents, has caused declines in fish populations in North Carolina. A biogeochernistry model appears to explain Se dynamics for several reservoirs. However, further work on sediment water interactions is needed to predict the speed of reservoir Se declines following cessation of inputs; 2) Mercury (Hg), volatilized in stack gases from coal fired power plants, is a public and wildlife health concern. Sediments play a major role in the biogeochernistry of Hg as documented in the Mercury Cycling Model (MCM); As with Se, questions about sediment water interactions limit the confidence in predictions about dynamics and effects of Hg; and 3) One of the recommendations from a recent Pellston Conference was to evaluate the use of a new paradigm as a basis for metals regulations. Under this new paradigm, effects of surface active metals (Ag, Al, Cd, Cu, Ni and Zn) on fish can be viewed as dependent on competition between the gill, a ‘biotic ligand’, and other environmental ligands for metals in discharges.Under this new paradigm, then, the mechanics of toxicity can he viewed as analogous to interactions at the sediment-water interface. It is clear from these three examples that fostering discussion among chemists and toxicologists, through joint participation at meetings and publication in journals used by both fields, is critical for development of accurate assessment capabilities and support of cost effective decision making.     

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.     

Determination of antagonism between cyhalofop-butyl and other rice (Oryza sativa) herbicides in barnyardgrass (Echinochloa crus-galli)

Herbicide antagonism is defined as the reduction of control of certain weeds as the result of applying mixtures of two or more herbicides. Cyhalofop-butyl, a graminicide used for postemergence grass weed control in rice, is antagonized by some rice herbicides when applied simultaneously. The result of this type of antagonism usually results in decreased control of grass weeds. Research has shown that herbicide antagonism between graminicides and other herbicides may be caused by different mechanisms as the result of activity of the tank-mix partner. Using HPLC, the objective of this experiment was to analyze the fate of cyhalofop-butyl in barnyardgrass tissue when applied alone and in combination with halosulfuron, propanil, or triclopyr. Results indicated that absorption of cyhalofop-butyl and hydrolysis to its phytotoxic metabolite, cyhalofop-acid, was rapid and that halosulfuron and triclopyr had no effect. Because of a likely interaction of propanil with an apoplastic esterase enzyme, increased levels of cyhalofop-butyl and cyhalofop-acid were detected in barnyardgrass tissue, indicating that cyhalofop-butyl metabolism was hindered by propanil.     

Interactions Between Sediments and Water Summary of the 7th International Symposium

The interactions between sediments and water have received increased emphasis over the last two decades, leading to a greater understanding of physical, chemical and biological processes in a wide range of aquatic systems including river, lake, estuarine and coastal systems. This new understanding has fostered research and assessment projects, and focused awareness on the implications of sediment/water interactions for policy and regulation. The international symposium on “The Interactions Between Sediments and Water” held in Baveno, Italy from 22–26 September 1996 was the seventh in a series of symposia held since 1976. All focused on issues relating to processes which occur near the sediment/water interface as well as responses to interactions between sediments and water. Previous symposia were held in Amsterdam in 1976, Kingston (Canada) in 1982, Geneva in 1984, Melbourne in 1986, Uppsala in 1990 and Santa Barbara in 1993. Almost 200 oral and poster presentations were made by attendees representing 27 nations, including dozens of participants from developing countries. The scientific sessions were organized around the following themes: sediment/water dynamics, contaminant interactions, sediment/nutrient relationships, sediments as historical records of deposition, sediment/water science in remote areas, sediment/organism interactions, and novel methods and analytical quality control. This paper attempts to summarize the key highlights of the various sessions.