title: Soil photolysis of herbicides in a moisture- and temperature-controlled environment.
abstract: The problem of maintaining the moisture content of samples throughout the course of a soil photolysis study is addressed. The photolytic degradations of asulam, triclopyr, acifluorfen, and atrazine were independently compared in air-dried soils and in moist (75% field moisture capacity at 0.33 bar) soils maintained at initial conditions through the use of a specially designed soil photolysis apparatus. Each pesticide was applied at 5 microg/g. The exposure phase extended from 144 to 360 h, depending on the half-life of the compound. A dark control study, also using moist and air-dried soils, was performed concurrently at 25 degrees C. The results showed significant differences in half-life. The dissipations generally demonstrated a strong dependence on moisture. In most cases, photolytic degradation on air-dried soil was longer than in the moist dark control soils. Half-lives in dry soil were 2-7 times longer, and in the case of atrazine, the absence of moisture precluded significant degradation. Moist soil experiments also tended to correlate more strongly with linear first-order degradations. The dark control experiments also demonstrated shorter half-lives in moist soil. Moisture was also observed to affect the amount of degradate formed in the soils.
authors.affiliation: Pittsburgh Environmental Research Laboratory, Inc., 3210 William Pitt Way, Pittsburgh, Pennsylvania 15238, USA.
authors.forename: Phillip
authors.initials: P
authors.lastname: Graebing
authors.forename: Michael P
authors.initials: MP
authors.lastname: Frank
authors.forename: J S
authors.initials: JS
authors.lastname: Chib
mesh_terms: D001280:Atrazine / Q000032:analysis; D002219:Carbamates / Q000032:analysis; D004787:Environmental Pollution; D006016:Glycolates / Q000032:analysis; D006207:Half-Life; D006540:Herbicides / Q000737:chemistry*; D006813:Humidity; D009579:Nitrobenzoates / Q000032:analysis; D010782:Photolysis; D012987:Soil / Q000032:analysis*; D013696:Temperature
chemical_list: D002219:Carbamates; D006016:Glycolates; D006540:Herbicides; D009579:Nitrobenzoates; D012987:Soil; C010036:asulam; C032742:triclopyr; C018425:acifluorfen; D001280:Atrazine