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EXTOXNET PIP-PARAQUAT http://acc.orst.cdu/cgi-bin/ints/01/pips/paraquat.hiin • Effects on birds: The compound is moderately toxic to birds, with reported acute oral LD50 values of 981 mg/kg and 970 mg/kg in bobwhite and Japanese quail, respectively [58]. The reported 5- to 8-day dietary LC50 value for the compound is 4048 ppm in mallards [58]. • Effects on aquatic organisms: Paraquat is slightly to moderately toxic to many species of aquatic life, including rainbow trout, bluegill, and channel catfish [58,8]. The reported 96-hour LC50 for paraquat is 32 mg/L in rainbow trout, and 13 mg/L in brown trout [58]. The LC50 for the aquatic invertebrate Daphnia pulex is 1.2 to 4.0 mg/L [8]. In rainbow trout exposed for 7 days to paraquat, the chemical was detected in the gut and liver, but not in the meat of the fish. Aquatic weeds may bioaccumulate the compound. In one study, 4 days after paraquat was applied as an aquatic herbicide, weeds sampled showed significant residue levels [87]. At high levels, paraquat inhibits the photosynthesis of some algae in stream waters [87]. • Effects on other organisms: Paraquat is nontoxic to honey bees [112]. Environmental Fate: • Breakdown in soil and groundwater: Paraquat is highly persistent in the soil environment, with reported field half-lives of greater than 1000 days [11,58]. The reported half-life for paraquat in one study ranged from 16 months (aerobic laboratory conditions) to 13 years (field study) [113]. Ultraviolet light, sunlight, and soil microorganisms can degrade paraquat to products which are less toxic than the parent compound. The strong affinity for adsorption by soil particles and organic matter may limit the bioavailability of paraquat to plants, earthworms, and microorganisms [1 1,58]. The bound residues may persist indefinitely and can be transported in runoff with the sediment. Paraquat is not significantly mobile in most soils [8]. That which does not become associated with soil particles can be decomposed to a nontoxic end product by soil bacteria [32]. Thus, paraquat does not present a high risk of groundwater contamination. Of 721 groundwater samples analyzed, only one contained paraquat, at a concentration of 20 mg/L [I I I]. • Breakdown in water: Paraquat will be bound to suspended or precipitated sediment in the aquatic environment, and may be even more highly persistent than on land due to limited availability of oxygen. It had a half-life in a laboratory stream water column of 13.1 hours [114]. In another study, paraquat dichloride was stable for up to 30 days [111]. In a third study of low levels in water, paraquat had a half-life of 23 weeks [I I I]. • Breakdown in vegetation: Paraquat dichloride droplets decompose when exposed to light after being applied to maize, tomato, and broad-bean plants. Small amounts of residues were found in potatoes treated with paraquat as a desiccant, and boiling the potatoes did not reduce the residue [8]. Physical Properties: • Appearance: Paraquat salts are colorless, white, or pale yellow crystalline solids, which are hygroscopic and odorless [1]. • Chemical Name: 1,1'-dimethyl-4,4'-bipyridinium [1] • CAS Number: 1910-42-5 • Molecular Weight: 257.20 • Water Solubility: 700,000 mg/L @ 20 C [1] • Solubility in Other Solvents: Dichloride salt is sparingly soluble in lower alcohols [1] • Melting Point: Decomposes @ 300 C [1] • Vapor Pressure: Negligible @ room temperature (paraquat dichloride) [1] • Partition Coefficient: 4.4683 [58] • AdsorptionCoefficient: 1,000,000 (estimated) [I I] of'4 511 100 4:1 1 PNI