Effects of esfenvalerate on the reproductive success of the bluegill sunfish, Lepomis macrochirus in littoral enclosures.

Adult bluegills were exposed to the synthetic pyrethroid esfenvalerate, during a reproduction study conducted in six littoral enclosures located in a 2-ha pond near Duluth, Minnesota. Bluegill reproductive success was determined after two applications of esfenvalerate at nominal concentrations of 0.0, 0.01, 0.08, 0.20, 1. 0, and 5.0 microg/L. Responses measured were adult behavior and spawning, embryo hatchability, larval survival until swim-up, young-of-the-year (Y-O-Y) growth, and total biomass. All adult bluegills died within one day following the first application at 5.0 microg/L. Successful spawning and resulting hatching of offspring were observed at all esfenvalerate concentrations except 5.0 microg/L. Following exposure at 1.0 microg/L, spawning was delayed for 15 days and few or no larvae survived. Bluegill Y-O-Y growth was reduced by 62, 57, and 86% in the 0.08, 0.20, and 1.0 microg/L esfenvalerate treated enclosures. Delayed adult spawning and reduced Y-O-Y growth may result in poor Y-O-Y overwinter survival which would result in a diminished or extirpated year class.

Effects of azinphos-methyl on the reproductive success of the bluegill sunfish, Lepomis macrochirus, in littoral enclosures.

Adult bluegills were exposed to a single application of azinphosmethyl in 12 littoral enclosures in a northern Minnesota pond. Responses measured were adult behavior and spawning, embryo hatchability, larval survival until swim-up, young-of-year (Y-O-Y) growth, and total biomass. Four enclosures each were treated at 1.0 and 4.0 micrograms/liter and four remained untreated. The half-life of azinphos-methyl was 2.3 and 2.4 days at each of the two treatment levels, respectively. Quantifiable residues remained in the water for 8 days. Concentrations of 4.0 or 1.0 microgram/liter did not cause any significant long-term (63 day) effects on bluegill reproduction, embryo hatchability, larval survival, growth, or biomass. Although important bluegill prey such as copepod nauplii and cladocerans were significantly or greatly reduced by Day 7 following treatment, they recovered to levels equal to or greater than some of the control enclosures by Day 35. The apparent lack of significant long-term effects on reproductive success can be partially explained by the relatively short half-life of azinphos-methyl in littoral enclosures.

Toxicity of chlorpyrifos, endrin, or fenvalerate to fathead minnows following episodic or continuous exposure.

Fathead minnow larvae (Pimephales promelas) were exposed to three individual pesticides during brief or continuous exposure in 96-hr and 28- to 30-day toxicity tests. Continuous exposure 96-hr LC50 values for chlorpyrifos, endrin, and fenvalerate were 122.2, 0.7, and 0.85 micrograms/liter, respectively. Continuous exposure chronic effect concentrations were chlorpyrifos, 2.1 micrograms/liter (increased deformities); endrin, 0.38 micrograms/liter (reduction in growth); and fenvalerate, 0.36 micrograms/liter (reduction in survival and growth). Brief exposure chronic test results indicated that fathead minnow exposure to chlorpyrifos for as few as 5 hr at a concentration similar to a continuous exposure 96-hr LC50 value resulted in increased deformities and a reduction in growth, whereas a 48-hr exposure at a concentration similar to a continuous exposure 96-hr LC50 value was required to cause a reduction in growth for endrin and a reduction in survival and growth for fenvalerate. It is suggested that although constant exposure laboratory tests are essential for hazard assessment, the relationships of exposure duration and toxicant intensity to ecotoxic effects are necessary for reliable risk assessments and implementation of water quality standards.

Acute and chronic toxicity of triphenyltin hydroxide to fathead minnows (Pimephales promelas) following brief or continuous exposure.

Fathead minnow larvae (Pimephales promelas) were exposed to triphenyltin hydroxide (TPTH) during brief (single pulse) or continuous exposure in 96-h and 30-day toxicity tests. The continuous exposure 96-h LC(50) value was 7.1 microg litre(-1). Brief exposures for 12 to 72-h gave 96-h LC(50) values that ranged from 61.8 to 6.0 microg litre(-1), respectively. The continuous exposure 30-day chronic effect concentration, based upon reduced growth, was 0.23 microg litre. Survival was significantly reduced at 2.0 microg litre(-1). Brief exposures for 24, 48, and 72-h in 30-day tests significantly reduced survival and growth at 13.0, 13.0 and 60.0 microg litre(-1) respectively. It is suggested that both toxicant concentration and exposure duration are important factors to consider in the risk assessment of potential pesticide hazards in the environment.