Mirex incorporation in the environment: Toxicity in two soil macroarthropods and effects on soil community respiration

The KD (knockdown dosage) and LD (lethal dosage) values of mirex were determined for the land isopod Armadillidium vulgare and the soil millipede Oxidus gracilis by feeding with a diet containing different concentrations of technical mirex powder. KD₅₀ and LD₅₀ values for A. vulgare at 10 days exposure were 11.6 ppm and 35.2 ppm, respectively; and for O. gracilis, 5.4 ppm and 198.7 ppm, respectively. The isopod A. vulgare was less susceptible to mirex poisoning as symptomized by knockdown behavior but was killed sooner than the millipede O. gracilis. Poisoned animals showed increased O₂ uptake after two to three days of feeding on mirex diet presumably due to increased muscular activity as induced by elevated oxidative metabolism. Technical mirex showed a significant effect on soil community respiration at 100 ppm concentration after 24 h but no change was observed at the higher concentrations of 500 and 1000 ppm. The addition of mirex as fire ant baits at the rate of 1:100, 1 : 1000, and I :10 000 bait to soil ratio also did not affect soil community respiration, but 02 uptake was nevertheless elevated due to the microbial population (bacteria and fungi) that immediately invaded the bait material.