Fate and impact of pesticides applied to potato cultures: the Nicolet River basin.

The fate of cash-crop (potato) pesticides was monitored from the fields on which they were applied to the nearby streams. The investigation took place in the Nicolet River basin in the province of Quebec, Canada. The main pesticides under study were aldicarb, fenvalerate, metribuzin, and phorate. Aldicarb was never detected in any of the samples. The other pesticides were all detected in soils at low concentrations. Only fenvalerate and metribuzin were detected in tile drain. Metribuzin concentrations of up to 0.25 microgram/g were detected in the soil giving rise to a concentration of 1.3 micrograms/liter in tile drain and 47.1 micrograms/liter in surface runoff. Low concentrations of metribuzin up to 0.41 microgram/liter were detected in the nearby streams. The CREAMS model simulating pesticide movement in the fields overestimated metribuzin losses in the runoff at a concentration of 107 micrograms/liter. The subsurface EXPRES model using a PRZM time series adequately estimated a metribuzin field subsurface runoff concentration of 0.5 microgram/liter. According to the Canadian Water Quality Guideline for the protection of aquatic life, the concentrations of pesticides found in surface waters of this potato-growing region of Quebec do not have a potential to impact on the aquatic life in these systems.

Comparative study of the effects of MCPA, butylate, atrazine, and cyanazine on Selenastrum capricornutum.

The herbicides MCPA, butylate, atrazine and cyanazine are extensively used in Canadian agriculture and information regarding their effects on indigenous biota is scarce. Phytotoxicity assessments were conducted in the laboratory on the common green alga Selenastrum capricornutum using both the active ingredient of the herbicides and their formulated products (for MCPA and butylate). Endpoints determined after the 96 h exposure included algal population growth inhibition (IC50-cell counts), percent lethality (LC50-flow cytometry derived) and photosynthetic electron transport inhibition (EC50-fluorescence induction). Pesticide formulations had greater toxic effects than the active ingredient alone. The 96 h IC50 (50% Inhibition Concentration) and LOEC (Lowest Observable Effects Concentration) using cell counts of S. capricornutum were 18.4 and 8.9 mg l(-1) respectively for MCPA-active ingredient and for MCPA-formulated, these were 0.62 and 0.0062 mg l(-1) respectively. Those for butylateactive ingredient were 61.0 and 8.3 mg l(-1) and for butylate-formulated 1.46 and 0.17 mg l(-1), respectively. The triazines active ingredient, which are photosynthetic inhibitors, had greater effects than either the MCPA or butylate. The IC50 for cyanazine and atrazine were 0.059 and 0.026 mg l(-1), respectively. By comparing the IC50 and LC50 values for the tested active ingredients, it was found that the effects of atrazine were algicidal, whereas those of cyanazine, butylate and MCPA were algistatic.

Environmental fate and effects of dicamba: a Canadian perspective.

Literature on the environmental fate and effects of the benzoic acid herbicide dicamba was reviewed to provide a scientific basis to derive Canadian Water Quality Guidelines. Included in the review was information on the uses and production of dicamba, its physical and chemical properties, environmental monitoring data in Canadian surface water and groundwater, soils, sediments, and biota, and its environmental degradation, persistence, and fate. Through monitoring, dicamba has been detected in less than 8% of surface-water samples to a maximum concentration of 13 micrograms.L-1, while 2% of groundwater samples were positive up to 517 micrograms.L-1. Only one study that analyzed sediments (with no detections) and no field studies that investigated residues in biota were found. Microbial degradation is the most important process governing the dissipation of dicamba in aquatic and soil environments. Photolysis, hydrolysis, volatilization, adsorption to sediment, and bioconcentration are not expected to be significant removal processes, based on limited environmental fate data. The half-life of dicamba in water is < 7 d, although residues have been detected in surface-water supplies in Alberta more than 6 mon after application. The literature reports the half-life in soils ranges from 4 to 555 d; however, < 12 wk would be typical under Canadian conditions. High moisture and temperature, and other conditions that favor microbial degradation, would likely reduce the half-life to < 4 wk. The principal soil and plant metabolite is 3,6-dichlorosalicylic acid, with minor amounts of 2,5-dihydroxy-3,6-dichlorobenzoic acid and 5-hydroxydicamba found. Dicamba is highly mobile in soil, and significant leaching is possible; its water solubility is 6.5 g.L-1 (25 degrees C) and it has a log octanol-water partition coefficient of 0.477. Acute and chronic toxicological studies for all nontarget plants and animals were also reviewed. The major groups of organisms for which toxicological data were collected were freshwater fish, invertebrates and plants, tame hays and cereals, legumes, and other crops, and livestock poultry and mammals. The acute toxicity (< or = 96-hr LC50) to freshwater fish ranged from 28 to 516 mg.L-1, whereas that for invertebrates ranged from 3.9 to > 100 mg.L-1. No chronic data were found for either of these groups. The chronic EC50 to 14 freshwater algae, based on growth inhibition, ranged from 100 to > 10,000 micrograms.L-1. No studies on freshwater macrophytes or any marine organisms were found. Agricultural crops exhibited varying toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Lemna minor membranes affected by adjuvants.

The perturbant effects of four Triton adjuvants, namely Triton X-15, X-35, X-100, and X-114 (alkyl aryl polyether alcohols), on some of the biochemical determinants of membrane integrity were determined under laboratory conditions. Two of these, Triton X-100 and X-114, are currently being assessed as emulsifiers for use in fenitrothion insecticidal formulations. Lemna minor L. plants were exposed to 40 microM (10-25 microg ml(-1) in 965 microg mg(-1) Dowanol (tripropylene glycol methyl ether) carrier solvent) adjuvant for a treatment time period of two weeks. A decrease in the contents of the total phospholipids and a concomitant increase in the contents of the galactolipids were found. No change was observed in the total lipid content. An unsaturation occurred in the fatty acids of the total lipids, phospholipids, and monogalactosyl diacylglycerides. This accounted for a significant decrease in palmitic and stearic acids and a concomitant increase in oleic, linoleic, and linolenic acids when these are compared with the fatty acids in the nontreated control sets. The fatty-acid profile of the digalactosyl diacylglycerides, however, differed only slightly from controls. Membrane-fatty-acid unsaturation suggests the possibility of a desaturase enzyme's being induced by these adjuvants.