Chronic toxicity of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in soil determined using the earthworm (Eisenia andrei) reproduction test

Abstract

The sublethal and chronic effects of the environmental contaminant and explosive octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in artificial soil were assessed using the earthworm (Eisenia andrei). Based on various reproduction parameters (total and hatched number of cocoons, number of juveniles and their biomass), fecundity was reduced at the different concentrations of HMX tested (from 280.0±12.3 to 2502.9±230.0 mg kg⁻¹ dry soil) in spiked artificial soil (LOEC: 280.0±12.3 mg kg⁻¹ dry soil). The growth of adult E. andrei was also reduced at the different concentrations tested, though no mortality occurred, even at the highest tested concentrations. The number of juveniles produced was correlated with the number of total and hatched cocoons, and the biomass of juveniles was correlated with the number of cocoons. Pooled results of these and earlier studies on explosives (TNT, RDX) using the E. andrei reproduction test confirm that effects of HMX on cocoon production are indicative of some reproductive consequences (number of juvenile and their biomass), whereas adult growth, in general, does not correlate strongly with change in reproduction capacity.

Introduction

Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX; high melting explosive) is commonly present in explosive-contaminated soil and groundwater (Guist et al., 1993, Simini et al., 1995, Hovatter et al., 1997; reviewed by Talmage et al., 1999). The environmental concentrations of HMX in soil on contaminated sites can range from 0.7 to 5700 mg kg⁻¹, whereas the groundwater and surface water ranged from 1.3 to 4200 and 1.9 to 67 μg l⁻¹, respectively (reviewed by Talmage et al., 1999). This explosive is toxic to some aquatic organisms, including fathead minnows (Pimephales promelas) and the freshwater microcrustacean Daphnia magna (reviewed by Talmage et al., 1999). HMX was not toxic to the bioluminescent bacteria Vibrio fisheri (liquid phase Microtox; Sunahara et al., 1998) and was not cytotoxic or mutagenic to bacterial and mammalian cells in aqueous solutions of HMX (Lachance et al., 1999).

HMX is also toxic to some terrestrial organisms including mice and rats (see review by Talmage et al., 1999). Lethal and sublethal effects (weight change) on earthworms (Eisenia fetida sp.) tested in soil containing different energetic substances (TNT, RDX, HMX) spiked soils have been reported earlier (Phillips et al., 1993, Robidoux et al., 1999a). An HMX concentration-dependent weight loss (14-day test) was detected in the earthworms and would indicate the possibility of sublethal effects, but no lethality was observed at concentrations of HMX up to 500 mg kg⁻¹ (Phillips et al., 1993). However, little or no information is available on the sublethal effects of explosives or their metabolites on soil invertebrates.

The effects of energetic substances on Eisenia sp. survival and weight changes have also been studied in explosives-contaminated soils. Phillips et al. (1993) showed that soil containing TNT (60 mg kg⁻¹), TNB (100 mg kg⁻¹), 2,4-DNT (125 mg kg⁻¹), and 2,6-DNT (40 mg kg⁻¹) was lethal to earthworms (14-day test). However, soils contaminated in part by HMX (50.7 kg⁻¹), RDX (55.9 mg kg⁻¹), and some TNT (0.8 mg kg⁻¹), 2,4-DNT (50.0 mg kg⁻¹) and 2,6-DNT (20.0 mg kg⁻¹) did not produce acute effects on earthworms.

Phillips et al. (1994) and Simini et al. (1995) evaluated the toxicity of soils samples from the Joliet Army Ammunition Plant. In these studies, these workers determined the survival rates and changes in biomass (live weight) in Eisenia sp. HMX concentrations correlated weakly with these endpoints. At this site, TNT was viewed as the primary toxic explosive in the soil. In other articles, Eisenia sp. were also used to study the lethal and sublethal effects of explosives-contaminated (including TNT, RDX and HMX residues) soils following composting (Gibbs et al., 1996, Gunderson et al., 1997, Jarvis et al., 1998).

The effects of TNT and RDX on earthworm reproduction have been recently shown (Robidoux et al., 1998, Robidoux et al., 1999b, Robidoux et al., 1999c, Robidoux et al., 1999d; Dodard et al., 1999). However, little is known on the reproductive effects of HMX in soil. Gunderson et al. (1997) have exposed E. fetida to an explosives (including TNT, RDX and HMX) compost-remediated soil. These workers showed that low concentrations of TNT, RDX and HMX (2.84,<2.9 and 3.91 mg kg⁻¹, respectively) in the composted soils did not affect the fecundity of the earthworms compared to composted non-contaminated soil.

Explosives in general, and HMX specifically, may decrease native earthworm populations and affect a higher trophic level of the food chain. This information would be helpful to future ecological risk assessments of explosives-contaminated sites. In the present study, the effects of HMX on growth and reproduction of Eisenia andrei in artificial soil were assessed.