Appendix 2 Open Literature Review Summaries for Malathion

As a negative control was not use, any potential effects from the use of a solvent could not be identified. A separate experiment was used to assess potential effects of the vehicle on mortality, but not on growth or behavioral endpoints. Also, based on the information provided, it is unclear whether a specific malathion treatment group was significantly different from control for growth rate (as wet weight). While significant decreasing trends in growth rates, based on wet weight or protein content, were reported, it appears that the pair-wise comparisons did not indicate any statistical significance between a specific treatment group and the control. As such, a definable NOAEC or LOAEC could not be determined. Also, while the test material source was reported, the impurity profile was not known relative to current standards.

Relyea, R.A. and N. Diecks. 2008. An unforeseen chain of events: lethal effects of pesticides on frogs at sublethal concentrations. Ecolog. App. 18(7): 1728-1742.

Two amphibian species, wood frogs (Rana sylvatica) and leopard frogs (Rana pipiens) were exposed to malathion along with peri- and phytoplankton and zooplankton at two different amphibian larvae densities (high and low) in aquatic mesocoms (approx. 1000L well water). Malathion (Malathion Plus (50%), Ortho Corporation) was applied to the mesocosms at a concentration of either 50 or 250 µg/L malathion applied either at the start of the study or four weeks after study initiation. A weekly application (from day 1 to 43) of 10 µg/L malathion was also included as a treatment group; a control group was also included. Chemical analysis of samples collected 1 hour after application and measured concentrations were 9.5 (weekly), 40 and 32 (50 µg/L, initial and later, respectively) and 300 and 190 µg/L (initial and later, respectively). The treatments were replicated four times for a total of 48 experimental units. A pond-drying component was added to the test design (removal of approx. 60L of water starting on day 62) and tadpoles that had not completed metamorphosis by day 79 were considered dead due to the effects of the pond drying. Amphibians eggs were collected (source not reported) and allowed to hatch on-site. Pond water was collected and tadpoles and invertebrate predators were removed and aliquots were added to each mesocosm along with 300 g dry leaves (primarily Quercus spp.) and 25 g of rabbit chow. Algae and zooplankton communities were in the cosms 18 days prior to addition of amphibians or malathion treatment. Twenty or 40 amphibian tadpoles (wood and leopard frogs, respectively) were added to each mesocosm (initial mass ± SE: wood frog = 68 ± 4 mg, leopard frogs = 91 ± 7 mg). On test day 15, temperature, pH, and dissolved oxygen were measured. The rate of sunlight decay with depth was measured on days 23 and 45. On day 8, 22 and 43, zooplankton was collected (0.2L tube sampler at 5 different locations in mesocosms, pooled, and screened) and total abundance was calculated in terms of cladocerans or copepods. Phytoplankton and periphyton abundance were measured on day 22 and 43 or 44 (phytoplankton: 500mL water, filtered and chlorophyll a concentrations measured; periphyton: removed from tiles, filtered and dry weight measured). Beginning on day 27 [first observance of a metamorph (wood frog)] until day 79, cosms were checked daily for metamorphs (removed when tail was <3 cm). The removed frogs were placed in 1L tubs with moss until complete tail resorption (GS 46). The study was terminated on day 79 and any remaining amphibians that had one emerged forelimb were allowed to complete metamorphosis; all others remaining were considered nonsurvivors. For the amphibians, survival, time to metamorphosis and body mass were analyzed. Multivariate analysis of variance (MANOVA) was used to evaluate control and treatment groups to test for effects of malathion, amphibian density as well as zooplankton and algae.

Based on the study authors, there was a reduction in zooplankton in all treatments which affected the other organisms (increase in phytoplankton and then decline in periphyton). For the wood frog, the study authors stated that the pesticide treatments did not affect the frogs compared to the control (possibly due to their short time to metamorphosis). However, for the leopard frogs, reductions in growth (18-22%, weekly and 250 µg/L treatments) and delayed development were observed, which led to subsequent mortality (43% decrease in survival in weekly treatment) as the mesocosms dried up.

The three treatments groups that had initial applications of malathion had significantly higher pH and dissolved oxygen values compared to the control.
For zooplankton, on the first and second sample date, the weekly and initial treatments had significantly reduced abundance of cladocerans (approx. reduced to 0%) compared to control; however, by the third sampling date, the treatments that received a weekly or later application had significantly reduced abundance (reduced to approx. 0%) whereas the treatments treated initially had recovered to values similar to the control (Figure 1). For the copopods, abundance in the treatment groups with the initial 50 or 250 µg/L dose was significantly reduced compared to the control (abundance approx. 0%) on the first sample date, but there were no differences on the second sample date and by the third sample date, copepod abundance in malathion treatments (all doses) were greater compared to control (Figure 1).

For phytoplankton, at the first sample date, the weekly and initial treatments had significantly greater abundance (approx. 50% increase) compared to control (Figure 2). On the second sample date, the treatments with either the initial or later applications of 50 µg/Lor initial application of 250 µg/L had significantly less phytoplankton (reduced approx. 30-70%) compared to control. The weekly application treatment group had significantly greater rates of light decay compared to control. For periphyton, on the first sample date, only the treatment with the initial dose of 50 µg/L had significantly reduced periphyton (Figure 3). At the second sample date, under high tadpole density, the treatments with the initial dose of malathion (50 or 250 µg/L) and weekly dose had 44–79% less periphyton compared to control.

Figure 1 (from Figure 3 in paper). Effects on zooplankton

Figure 2 (from Figure 4 in paper). Effects on phytoplankton

Figure 3 (from Figure 5 in paper). Effects on Periphyton

Figure 4 (from Figure 6 in paper). Effects on Amphibians