Dose-related effects following oral exposure of 2,4-dinitrotoluene on the western fence lizard, Sceloporus occidentalis

Abstract

2,4-dintitrotoluene (2,4-DNT) is an explosive frequently found in the soil of military installations. Because reptiles can be common on these sites, ecological risk assessments for compounds such as 2,4-DNT could be improved with toxicity data specific to reptiles. Western fence lizards, Sceloporus occidentalis, were used to develop a laboratory toxicity model for reptiles. A hierarchical approach was used; acute to subchronic studies were conducted to provide toxicity data relevant to short- and long-term exposures. First, a modified median lethal dose (LD50) study was conducted on male and female lizards using a stage-wise probit model. The LD50 was 577 mg/kg for female and 380 mg/kg for male lizards. Subsequently, a subacute experiment was conducted to further assess 2,4-DNT toxicity to male lizards and to define exposure levels for a longer term, subchronic study. The subchronic study was conducted for 60 consecutive days; male lizards were exposed to 0, 9, 15, 25, 42, 70 mg/kg/d. Dose-dependent mortality was observed in the three highest dose groups (25, 42, and 70 mg/kg/d); all other animals survived the study duration. Benchmark dose model calculations based on mortality indicated a 5% effect level of 15.8 mg/kg/d. At study termination, a gross necropsy was performed, organ weights were taken, and blood was collected for clinical and hematological analysis. Body weight, kidney weight, food consumption, postdose observations, and blood chemistries all were found to be significantly different from controls at doses above 9 mg/kg/d. Also, preliminary results suggest behavioral observations, and reduced food consumption may be a sensitive indicator of toxicity. The present study indicates Sceloporus occidentalis is suitable for evaluating toxicity of compounds to reptilian species.

Scientific Opinion on the state of the science on pesticide risk assessment for amphibians and reptiles

“…The rearing of western fence lizards continued for many years and contributed to a large portion of the acute toxicity data for reptiles (e.g., McFarland et al, 2008McFarland et al, , 2009Suski et al, 2008;Salice et al, 2009;Weir et al, 2015Weir et al, , 2016b. Throughout this period, there has been an effort to improve the dosing methods of fence lizards continuing the goal of a standardised toxicity test for reptiles (Suski et al, 2008;Salice et al, 2009;Weir et al, 2015). Specific methods have been developed for acute and chronic toxicity with reptiles (Suski et al, 2008;Salice et al, 2009) as well as oral dosing methods (Suski et al, 2008;Weir et al, 2015).…”

“…Standard oral exposure methods for reptiles should be similar to those already in place for birds and mammals. These tests could be adapted to reptiles with special considerations for dosing that have been previously investigated (Suski et al, 2008;Weir et al, 2015). Development of either acute or chronic oral exposure tests for reptiles would require the availability of a model species and potentially optimising husbandry methods to create high turnover.…”

Development of a 2,4-Dinitrotoluene-Responsive Synthetic Riboswitch in E. coli cells

“…2,4-Dinitrotoluene is an explosive chemical that is used in the production of the polyurethane foam for bedding and furniture industries and as a gelating agent in explosives, ammunition, and dyes 12 . The detection of DNT is important for a few reasons.…”

Unraveling the Relative Importance of Oral and Dermal Contaminant Exposure in Reptiles: Insights from Studies Using the Western Fence Lizard (Sceloporus occidentalis)

“…The method has been described previously [8], [10]. Rather than intubate the lizards, repeatable and accurate dosing can be achieved with a micropipette and the technique is presumably less stressful for the animal.…”

“…The introduction of the western fence lizard ( Sceloporus occidentalis ) as a vetted model organism for reptile ecotoxicity studies [7] has played a large role in increasing the availability of reptile toxicity data in recent years for metals [8], pesticides [9], and compounds of military importance [10], [11]. However, both estimates of exposure and estimates of toxicity are needed to conduct meaningful ERAs.…”