The degradation and leaching potential of the herbicide [14C]glufosinate-ammonium [the ammonium salt of dl-homoalanin-4-yl(methyl)phosphinic acid] in a northern Ontario forest environment were examined. The DT50 and maximum leaching depth were 4.3 days and 10 cm (humic layer), respectively. [14C]MPPA-3 (3-methylphosphinylpropionic acid) and [14C]MPAA-2 (2-methylphosphinylacetic acid), the two main metabolites of glufosinate-ammonium, also did not leach beyond 10 cm. At 32 days postapplication, approximately 10−20% of the parent and metabolites remained in the soil, but by the following season (day 295) residue levels had declined to near zero. Keywords: Glufosinate-ammonium; forestry; persistence; leaching potential

Abstract-The impact of glufosinate-ammonium and bialaphos on the zooplankton community in a small eutrophic lake was investigated using in situ enclosures. Concentrations inducing a 20% reduction in abundance (EC20), as interpolated from best-fit, nonlinear regression analyses were similar for both herbicides and ranged from 0.03 to 0.16 mg/L for various zooplankton taxa. Similarly, median effective concentrations (EC50) estimates ranged from 0.12 to 0.50 mg/L. Thus, toxicity endpoints overlapped and in some cases were well below expected environmental concentrations calculated for accidental direct overspray (1 mg/L) or drift events (0.25 mg/L). Significant concentration-dependent reductions were observed within the first 2 weeks following application and for a number of taxa persisted throughout the observation period (63 d posttreatment). At the highest treatment level, (10 mg/ L), negative impacts were still apparent in the year following treatment. The results of this field study, which demonstrate significant negative effects on a variety of zooplankton taxa at environmentally relevant concentrations and relatively slow recovery therefrom, suggest a substantial risk of sustained adverse impacts on the zooplankton communities should these herbicides contaminate shallow lentic ecosystems. Extensive mitigative measures are required to protect such water bodies from potential impacts of phosphinothricinbased herbicides.

The effects of tebufenozide (RH-5992), a potential forest insecticide, on zooplankton communities were determined in 16 littoral enclosures in a small forest lake of northern Ontario. Community structure in enclosures treated with 9, 36, or 157 µg tebufenozide/L ( 0.2, 0.7, and 3 times the expected environmental concentration) was compared with natural zooplankton communities in control enclosures. No significant treatment effects on zooplankton communities were detected, even at 3 times the expected environmental concentration. While some changes in community structure of crustacean zooplankton in enclosures occurred through the season, these did not appear to be related to the tebufenozide treatments. Tebufenozide residues in water dissipated following exponential decline kinetics with time to 50% dissipation (DT50) ranging from 32 to 35 days irrespective of initial concentration. There were no differences in pH, dissolved oxygen, conductivity, and phytoplankton abundance among treatment levels (repeated-measures ANOVA, p > 0.07).

Abstract-A rapid, two-stain (fluorescein diacetate and ethidium homodimer-1) flow cytometric assay to evaluate viability and cytotoxicity of the alga Selenastrum capricornutum in preserved samples is described. For storage, stained cells were fixed in glutaraldehyde, flash frozen in liquid nitrogen, and stored frozen (Ϫ20ЊC) for assessment at a later date. Weekly analysis of frozen samples showed that fluorescence was stable for 7 weeks. A mixture of 50% healthy and 50% heat-killed cells of S. capricornutum showed 36.1% healthy cells, 13.2% compromised cells, 12% nonstained cells, and 38.7% dead cells. This technique was tested using sodium dodecyl sulfate (SDS) and phenol as toxicants. Threshold concentrations for toxicant impact were in the range of 1 to 10 mg/L for SDS and 10 to 100 mg/L for phenol. Estimates of mortality showed 96-h median lethal concentration (LC50) values of 2,340 mg/L and 6,970 mg/L for SDS and phenol, respectively. This two-stain flow cytometric procedure has proven to be a reliable, sensitive assay for determining viability of S. capricornutum in preserved samples. The sensitivity of this dual-color assay and the ability to store samples for later analysis are significant improvements over current techniques.