Glenn W. Stratton

Effects of synthetic pyrethroid insecticides on nontarget organisms

Pyrethroids1 are among the most potent insecticides known. They are synthetic compounds structurally derived from pyrethrin I, one of the six active components of pyrethrum, which is an extract from the dried flower heads of Chrysanthemum cinerariaefolium. The natural pyrethrins have excellent insecticidal properties and low mammalian toxicity, but are of limited use because of their low photostability and high biodegradability (Wouters and van den Bercken 1978). However, pyrethroids are relatively stable, have a high toxicity to a wide spectrum of insects (Elliott 1976), are relatively nontoxic to mammals (Elliott 1976), and have tremendous agricultural potential (Harris and Turnbull 1978). Moreover, pyrethroids are much less persistent than the organochlorine insecticides, such as DDT and dieldrin, and apparently do not accumulate in the environment.

Effects of the herbicide atrazine and its degradation products, alone and in combination, on phototrophic microorganisms

Toxic effects of the herbicide atrazine and four of its degradation products were determined for growth, photosynthesis, and acetylene-reducing ability of two species of green algae and three species of cyanobacteria. Atrazine was significantly more toxic than its degradation products towards the above test criteria, yielding EC50 values ranging from 0.1 to 0.5 ppm (μg/ml) for photosynthesis and 0.03 to 5.0 ppm for growth. Deethylated atrazine was the next most toxic with EC50 values of 0.7 to 4.8, and 1.0 to 8.5 ppm for photosynthesis and growth, respectively. With deisopropylated atrazine the EC50 values for the same physiological functions ranged from 3.6 to 9.3, and 2.5 to >10 ppm, respectively. Hydroxy- and diamino-atrazine were non-toxic towards most of the cultures tested. Acetylene reduction with cyanobacteria was found to be insensitive to all of the test compounds, except for atrazine, which had an EC50 of 55 ± 15 ppm towardsAnabaena inaequalis. Combinations of atrazine and its monodealkylated products were tested withA. inaequalis and yielded both synergistic, antagonistic, and additive interaction responses, depending upon the actual test system employed.

Growing season surface water loading of fecal indicator organisms within a rural watershed

The loading of microbial contaminants was examined within the Thomas Brook watershed, a 784 ha mixed land-use catchment located in the headwaters of the Cornwallis River drainage basin (Nova Scotia, Canada). The objectives were to: (i) examine spatial and temporal characteristics of fecal bacteria loading during the growing season from five subwatersheds, and (ii) develop areal fecal indicator organism export coefficients for rural landscapes. Fecal coliform, Escherichia coli, total suspended solids (TSS) concentrations and stream flow were monitored at five locations in the watershed over six consecutive growing seasons (May-Oct, 2001-2006). A nested watershed monitoring approach was used to determine bacterial loading from distinct source types (residential vs. agricultural) during both baseflow and stormflow periods. Areal bacterial loading rates increased in each nested watershed moving downstream through the watershed and were highest in the three subcatchments dominated by agricultural activities. Upper watershed bacterial loading throughout the growing season from an agricultural subcatchment (Growing Season Avg 8.92 x 10(10) CFU ha(-1)) was consistently higher than a residential subcatchment (Growing Season Avg 8.43 x 10(9) CFU ha(-1)). As expected, annual average stormflow bacterial loads were higher than baseflow loads, however baseflow loads still comprised between 14 and 35% of the growing season bacterial loads in the five subwatersheds. Fecal bacteria loads were greater during years with higher annual precipitation. A positive linear relationship was observed between E. coli and TSS loading during the 2005 and 2006 growing seasons when both parameters were monitored, indicating that the processes of sediment transport and bacterial transport are linked. It is anticipated that computed areal microbial loading coefficients will be useful in developing watershed management plans. More intensive sampling during stormflow events is recommended for improving these coefficients.

Year-round treatment of dairy wastewater by constructed wetlands in Atlantic Canada

Constructed wetlands are used throughout North America to treat various types of wastewater in warm climates; however, little has been documented about their treatment processes and efficiencies during winter periods in Atlantic Canada. Two small-scale constructed wetlands (100 m2) of differing operational depth (wetland 1: 0.15 m shallow zone depth and wetland 2: managed water level) were designed to treat agricultural wastewater at the Bio-Environmental Engineering Center of the Nova Scotia Agricultural College. Both wetlands were monitored from November 2000 through March 2002 to evaluate treatment efficiencies and mass reductions of five-day biological oxygen demand (BOD5), total suspended solids (TSS), total phosphorus (TP), and ammonia-nitrogen (NH3-N). An average loading rate of 44.7 kg BOD ha−1 d−1 was loaded into each wetland, even during winter months. Percent removal and mass reductions for BOD5, TSS, TP, and NH3-N in both wetlands, irrespective of water levels, ranged from 62 to 99%. The treatment of TP was not found to be as effective as the other parameters, especially during high loading periods. Results show promise for the operation of constructed wetlands on a year-round basis in Atlantic Canada.

Gas emissions from straw covered liquid dairy manure during summer storage and autumn agitation.

This study evaluated the effect of straw covers on emissions from liquid manure during storage and agitation. Emissions of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ammonia (NH3) were measured from six tanks (6.6 m2 each) containing batch-loaded liquid dairy manure. This was conducted between June and October 2007 in Nova Scotia, Canada. Straw was added to four of the tanks at two thicknesses (15 and 30 cm), while two tanks remained uncovered. Gas concentrations were measured using tunable diode lasers, an infrared gas analyzer, and acid traps. Fluxes were measured using steady-state chambers. At the end of the study, one tank from each treatment was agitated. During 122 d of undisturbed storage, the covers increased emissions of CO2 and N2O. However, the 15 and 30 cm covers reduced CH4 emissions by 24% and 28% and reduced NH3 emissions by 78% and 90%, respectively. During 5 d of intermittent agitation, substantial releases of CO2, CH4, and NH3 were observed from all treatments. In this period, greenhouse gas emission reductions were relatively unchanged because releases from the control and covered tanks were similar. However, emissions of NH3 during agitation were highest from tanks that had been covered, thereby decreasing the overall emission reduction provided by the 15 and 30 cm covers to 68% and 76%, respectively. Despite elevated emissions during agitation, the results suggest that straw covers provide an overall reduction of CH4 and NH3 emissions compared to the control.

The influence of solvent type on solvent-pesticide interactions in bioassays

The effect of solvent type on solvent-pesticide interactions was examined by interacting the fungicide captan with the solvents acetone, ethanol, methanol, hexane, dimethyl sulfoxide (DMSO), andN,N-dimethylformamide (DMF), using growth of the fungiPythium ultimum, Sclerotinia homeocarpa, andPestalotia sp. as a toxicity criterion. DMF, ethanol, and methanol were generally the most toxic solvents tested, yielding EC50 values from 0.51 to 2.29% (v/v). The least toxic solvent was hexane, with EC50 values up to 36.60% (v/v). Acetone and DMSO evidenced median toxicity, yielding EC50 values of 1.99 to 12.07% (v/v). WithP. ultimum andS. homeocarpa, captan interacted synergistically with all solvents tested except hexane, with the actual solvent concentration at which synergism occurred being dependent upon the level of captan. Hexane interacted additively with 2.5 ppm captan towardsS. homecarpa, antagonistically with 5.0 ppm captan towardsP. ultimum and synergistically with captan in all other combinations tested. WithPestalotia sp., captan interacted antagonistically with acetone, ethanol, and methanol, and synergistically with hexane, DMSO, and DMF. Captan was more toxic towardsP. ultimum when dissolved in DMSO, and less toxic in the presence of hexane and DMF. WithS. homeocarpa, captan was more toxic with ethanol and DMSO, and less toxic when dissolved in acetone, methanol, and hexane. DMSO and hexane elicited less toxicity from captan when tested towardsPestalotia sp., while acetone, ethanol, and methanol elicited the greatest toxicity.

Greenhouse gas emissions from surface flow and subsurface flow constructed wetlands treating dairy wastewater.

Agricultural wastewater treatment is important for protecting water quality in rural ecosystems, and constructed wetlands are an effective treatment option. During treatment, however, some C and N are converted to CH(4), N(2)O, respectively, which are potent greenhouse gases (GHGs). The objective of this study was to assess CH(4), N(2)O, and CO(2) emissions from surface flow (SF) and subsurface flow (SSF) constructed wetlands. Six constructed wetlands (three SF and three SSF; 6.6 m(2) each) were loaded with dairy wastewater in Truro, Nova Scotia, Canada. From August 2005 through September 2006, GHG fluxes were measured continuously using transparent steady-state chambers that encompassed the entire wetlands. Flux densities of all gases were significantly (p < 0.01) different between SF and SSF wetlands changed significantly with time. Overall, SF wetlands had significantly (p < 0.01) higher emissions of CH(4) N(2)O than SSF wetlands and therefore had 180% higher total GHG emissions. The ratio of N(2)O to CH(4) emissions (CO(2)-equivalent) was nearly 1:1 in both wetland types. Emissions of CH(4)-C as a percentage of C removal varied seasonally from 0.2 to 27% were 2 to 3x higher in SF than SSF wetlands. The ratio of N(2)O-N emitted to N removed was between 0.1 and 1.6%, and the difference between wetland types was inconsistent. Thus, N(2)O emissions had a similar contribution to N removal in both wetland types, but SSF wetlands emitted less CH(4) while removing more C from the wastewater than SF wetlands.

Permeable Synthetic Covers for Controlling Emissions from Liquid Dairy Manure

Liquid manure storages emit greenhouse gases (GHGs) and ammonia (NH3), which can have negative effects in the atmosphere and ecosystems. Installing a floating cover on liquid manure storages is one approach for reducing emissions. In this study, a permeable synthetic cover (Biocap™) was tested continuously for 165-d (undisturbed storage + 3-d agitation) in Nova Scotia, Canada. Covers were installed on three tanks of batch-loaded dairy manure (1.3 m depth × 6.6 m2 each), while three identical tanks remained uncovered (controls). Fluxes were measured using steady-state chambers. Methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) were measured by absorption spectroscopy, and NH3 was measured using acid traps. Results showed covered tanks consistently reduced NH3 fluxes by approximately 90%, even though a surface crust formed on controls after about 50 days. Covers continued to reduce NH3 flux during agitation. Covered tanks also emitted significantly less CO2 and N2O than the controls (p-value <0.01). However, CH4 fluxes were not reduced, and therefore overall GHG fluxes were not substantially reduced. Short-term trends in CH4, CO2, and N2O flux provided insight into cover function. Notably, bubble fluxes were a key component of CH4 emissions in both treatments, suggesting the covers did not impede CH4 transport.

Interaction of organic solvents with the green alga Chlorella pyrenoidosa.

Solvents are often a component of bioassay systems when water-insoluble toxicants are being tested. These solvents must also be considered as xenobiotics and therefore, as potential toxicants in the bioassay. However, the effects of solvents on the organisms being tested and their possible interaction with the test compound are often overlooked by researchers. The purpose of the present study was to compare the inhibitory effects of six solvents commonly used in pesticide bioassays towards growth of the common green alga Chlorella pyrenoidosa, and to examine the occurrence of solvent-pesticide interactions with this organism.

Comparison of methods for the extraction of pentachlorophenol from aqueous and soil systems

Abstract The efficiency of extraction of pentachlorophenol (PCP) from both soil and a liquid bacterial growth medium was evaluated using a standard extraction procedure and three alternative methods for each system. Significant differences in recovery efficiency and time/cost factors were noted in both test systems. In the bacterial medium, a column extraction procedure was significantly more effective than the standard method. In soil, the alternative procedures were as effective as the standard method at extracting PCP, but offered substantial time and cost savings.