Toxicity of the explosive metabolites hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) and hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) to the earthworm Eisenia fetida

Toxicity of hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) to earthworm was evaluated. Both MNX and TNX had lethal and sublethal effects on earthworms. Exposure to MNX- or TNX-contaminated soil caused a significant concentration-dependent decrease in earthworm survival and growth. The lowest observed lethal concentration (LOLC) for both MNX and TNX was 100 and 200 mg kg−1 soil dry weight in the sandy loam soil and in the silt loam soil, respectively. No earthworms survived for 14 days in MNX- or TNX-spiked soil at 500 mg kg−1 soil dry weight. After 7 days exposure, the lowest observed effect concentration (LOEC) for earthworm growth was 50 mg kg−1 soil dry weight for TNX and 100 mg kg−1 soil dry weight for MNX in both soil types. The LC20 and LC50 for MNX in sandy loam soil were 114 and 262 mg kg−1 and for TNX, they were 114 and 254 mg kg−1 soil dry weight, respectively. The corresponding values for MNX and TNX in silt loam soil were 234 and 390 mg kg−1 soil dry weight, respectively, and 200 and 362 mg kg−1 soil dry weight, respectively. After 35 days exposure, earthworm growth was reduced 8–39% by TNX in sandy loam soil, whereas TNX only inhibited earthworm growth 5–18% at the same concentration range in silt loam soil. LC20 and LC50 for TNX were slightly lower than for MNX; this indicates that TNX was more toxic than MNX. No significant morphological or developmental abnormalities were observed in earthworms surviving exposure.