James E. Woodrow

Evaluation of a gas chromatographic method calculating vapor pressures with organophosphorus pesticides

Abstract The vapor pressures of 20 organophosphorus pesticides varying widely instructure, polarity and volatility were calculated using a method based upon gas chromatographic (GC) retention data. For seven of the pesticides, vapor pressures were determined experimentally by a standard gas saturation method for comparison with the GC-calculated values. Several experimental variables, including the number of GC temperatures and spread between them, nature of the liquid phase in either packed or capillary columns, and nature of the reference compound, were studied for their influence on the GC methods error. The GC calculation, using a short SE-30 capillary column, single reference compound (methyl parathion), and melting point correction for those test compounds which are solids at room temperature, provided vapor pressures agreeing with an average factor of approximately 4 with experimental vapor pressures. The agreement improved when the comparison was with test compounds which are liquids at room temperature and when the polarity of the GC reference compound approximated that of the test compounds.

Airborne and surface residues of parathion and its conversion products in a treated plum orchard environment

Airborne pesticide residues were collected both within and downwind from a parathion-treated plum orchard by high volume sampling through XAD-4 macroreticular resin. Levels of paraoxon in excess of 100 ng/m3 were found in orchard air, along with parathion, during the early days of two 21-day sampling studies. Paraoxon:parathion ratios in the orchard air were relatively constant, averagingca. 0.5 for days 1 to 21 following treatment. Likely sources of airborne paraoxon include vaporization and dislodgement from soil and leaf surfaces, and chemical conversion of parathion in the air. Support for the latter came from observation of an increased paraoxon:parathion ratio in air samples collected downwind from the orchard. Atmospheric conversion of parathion to paraoxon, accelerated by sunlight, was indicated by both field and laboratory studies. Overall dissipation of parathion from the orchard air, soil, and leaf tissue proceeded to a considerable extent through breakdown to paraoxon under the dry climatic conditions of these studies. Eventual conversion to the relatively stable breakdown product,p-nitrophenol, was indicated from analysis of air in the orchard vicinity.

Acrylamide release resulting from sunlight irradiation of aqueous polyacrylamide/iron mixtures.

Linear anionic polyacrylamide (PAM) has been used in irrigation practices as a flocculating agent to minimize water losses through seepage in earthen canals. The stability of PAM is of concern because of the possibility of acrylamide (AMD) monomer release during environmental weathering. Aqueous solutions of commercial PAM mixed with ferric sulfate, subjected to simulated and natural sunlight irradiation, showed polymer chain scission and release of the AMD monomer. At acid/neutral pH, the amount of AMD released was directly related to the concentration of ferric ion and the irradiation time. At alkaline pH (approximately 8), PAM/Fe(3+) mixtures were stable under irradiation. PAM chain scission involved the hydroxyl radical, but specific AMD release appeared to require PAM-bound iron. Low iron concentrations and alkaline pH of irrigation water would limit AMD release. Residual monomer in PAM can contribute AMD to irrigation water, but concentrations would remain below the U.S. EPA drinking water standard of 0.5 ppb.

Sampling and analysis of airborne residues of paraquat in treated cotton field environments.

A method was developed for the analysis of paraquat residues in airborne particulate matter collected by filtration or impaction. The method is based on extraction of paraquat with 6N hydrochloric acid, transfer of residue to saturated ammonium bicarbonate solution, and reduction of the resulting residue with alkaline sodium borohydride to a mixture of two tertiary amines with subsequent determination by nitrogen-selective gas chromatography (GLC). Recoveries ranged from 74 to 96% for filters spiked at 0.05 microgram and above; the limit of detection is approximately 0.5 ng/m3 for high volume air samples. Paraquat concentrations measured in the air downwind from two commercial applications to cotton during spraying fell regularly from extrapolated interval-average values of 4.31 and 10.7μg/m3 at the 1 m downwind edge of the two fields to <50 ng/m3 at approximately 400 m downwind. Downwind samples taken 2 to 4 hr after spraying contained 1 to 10% as much paraquat as those during spraying, and by 5 to 7 hr no paraquat was detectable in the downwind air. Paraquat was also found in the airborne particulate matter during mechanical harvesting of one of the fields, the maximum interval-average values being 1,245 and 516 ng/m3 just outside and inside an open cab, respectively. The analytical findings for paraquat are compared with those forS,S,S-tributylphosphorotrithioate (DEF®), a component of the harvest aid mixture employed, and discussed in terms of occupational exposure, potential hazard, and recommended occupational practices.

Accumulative sampling of trace pesticides and other organics in surface water using XAD-4 resin

Abstract XAD‐4 resin accumulative sampling was tested as a means of on‐site extraction of surface waters. Recoveries for most organochlorine, organophosphorus, organonitrogen, chlorophenol, and chlorophenoxy acid pesticides and related pollutants were acceptable (>50%) when spiked at the 10 and 0.1 ppb levels. Detection limits of 1–100 ppt were attainable for most compounds in river water, although lower levels required the use of an HPLC cleanup/fractionation step prior to those GC determinations using electron‐capture detection. XAD‐4 accumulative sampling was competitive with solvent extraction of grab samples in terms of recoveries, and offered advantages in volume of water sampled, detection limits, and sample handling. The wide range of solute applicability combined with the ease of constructing and operating the accumulative sampler recommends it over grab sampling for many types of monitoring applications.

Models for assessing the volatilization of herbicides applied to flooded rice fields

Abstract Volatilization rates of MCPA, thiobencarb, and molinate from water were calculated using the EXAMS aquatic fate computer model, and measured in a laboratory chamber and in flooded rice fields. A fair to good correlation was obtained between EXAMS-calculated and chamber-measured rates for all three herbicides. Field-measured values correlated well with chamber-measured rates for thiobencarb and molinate. For MCPA, field-measured values were much higher than expected for volatilization from water alone. In this case, the presence of plant and other surface residues in the field made the major contribution to observed volatilization. For MCPA, 4-chloro-o-cresol flux was comparable to that of the parent herbicide.

Degradation of pesticide waste taken from a highly contaminated soil evaporation pit in California

The primary methods for disposing of liquid pesticide wastes in California has been the dumping of the liquid materials into soil evaporation pits, ditches, and ponds. Many, if not most of these systems are unlined and have been in use for many years. One such soil pit located in northern California was found to be highly contaminated with an estimated level of >1 kg of active pesticide per 0.1 m3 of top soil. The top few cm of the bed contained an organic layer resembling slightly decomposed straw. The soil underlying the organic layer was clay, similar in texture to that typically found in rice growing areas. Both of these soil types were removed from the evaporation pit and placed in trays along side trays containing a similar soil type but free of pesticides. These latter trays were fortified with six pesticides and subjected to various soil amendments, including organic matter, lime, acids, and nutrients, under moist and flooded conditions for purposes of determining the optimum conditions for degrading high concentrations of pesticides in these soils. The effect of the soil amendments on the pesticide-fortified soils were generally pesticide dependent. The pH of the soils was a major factor in degradation but was different between the anaerobic and aerobic soils. Half lives of most pesticides was shorter with the highest pH soils under anaerobic conditions while the opposite was true with the aerobic treatments. The contaminated soils removed from the evaporation pit and treated with manure, ammonium phosphate and lime were very effective in reducing the half lives of the pesticides in both aerobic and anaerobic soils, as compared to corn meal and ammonium phosphate treatment. Alternating between moist and flooded soil conditions plus a heavy lime treatment combined with an organic source such as manure should provide an effective treatment for degrading pesticides in a contaminated toxic waste site.

Comparison of headspace and gas-stripping methods for determining the Henry's law constant (H) for organic compounds of low to intermediate H

A computer-controlled headspace sampling and gas chromatographic system (HS-GC) was used to measure Henrys Law constant (H) for organic compounds. The HS-GC results, extrapolated to ambient temperature in Clausius-Clapeyron type equations, compared well with values obtained using a gas-stripping method at ambient temperature. The HS-GC method provided the temperature-dependence of H so that it can be calculated at any temperature, which is essential when comparing laboratory results with values of H derived from air/water distributions in the environment.

Quantitative integration of the Salmonella microsuspension assay with supercritical fluid extraction of model airborne vapor-phase mutagens

Vapor-phase mutagens are potentially a major class of toxic contaminants in ambient and indoor air. These compounds are not routinely analyzed due to a lack of an established integrated methodology to quantitatively trap, extract and test the compounds in a bioassay. In a previous report, we emphasized the trapping of volatile and semi-volatile mutagens and the extraction of these compounds using supercritical carbon dioxide (CO2). In the present study, we discuss the use of a bioassay for the quantitation of the model mutagens, ethylene dibromide(EDB) and 4-nitrobiphenyl (4-NB), trapped from an airstream. The compounds EDB and 4-NB were released into a controlled airstream, trapped on XAD-4 adsorbent, and were extracted using supercritical CO2. The extract was tested in a microsuspension modification of the Ames Salmonella/microsome test adapted for volatile compounds. Linear dose-response relationships were obtained for supercritical CO2-extracted EDB using tester strain TA100 (+/- S9) and for 4-NB using tester strains TA98 and TA100 (-S9). Standard dose-response curves with known amounts of the compounds were also determined for comparison with measured amounts of the model compounds collected in an airstream. The gas chromatographic (GC)- and bioassay-determined quantities of EDB and 4-NB were highly correlated, accurate and precise. For example, bioassay-determined EDB concentrations were within 10% of the GC-determined concentrations. Our results demonstrate that the integrated methodology for vapor-phase mutagens developed in this study would be useful for quantitative analysis of these and related airborne vapor-phase mutagenic compounds.

Vapor-pressure measurement of complex hydrocarbon mixtures by headspace gas chromatography

Abstract Headspace gas chromatography was used to measure the vapor pressures of single n -alkane hydrocarbons and their binary, ternary and quaternary mixtures at various temperatures in the range 38–107°C. In addition, diesel fuel, gasoline and crude oil vapor pressures were measured at 38 and 70°C. The microprocessor-controlled headspace gas chromatograph automatically thermostated the samples contained in septum-sealed glass vials to equilibrate the vapor and liquid for a pre-set period of time (usually 60 min), pressurized the vials to a pre-set pressure (at least 138 kPa gauge) by inserting a hollow needle through the septum, and sampled the vapor for a pre-set period of time (0.01 min) by allowing the pressure in the vial to drive an aliquot of the vapor ( ca. 9 μl) through the needle and onto the analytical column. Using this technique, single n -alkane hydrocarbon vapor pressures, measured by totally vaporizing μl aliquots in the vials, agreed, on the average, to within 1% with calculated values based on hydrocarbon properties. Likewise, measured total vapor pressures of the binary, ternary, and quaternary mixtures compared well with calculated values, assuming ideal behavior for the mixtures, and the measured vapor pressures of diesel fuel, gasoline, and several crude oils showed good precision and accuracy.