A battery of toxicity tests as indicators of decontamination in composting oily waste.

Heterogeneous oily waste from an old dumping site was composted in three windrows constructed from different proportions of waste, sewage sludge, and bark. The objectives of this pilot study were to examine the usefulness of composting as a treatment method for this particular waste and to study decontamination in the composting process by using a battery of toxicity tests. Five samples from the windrow having intermediate oil concentrations were tested with toxicity tests based on microbes (Pseudomonas putida growth inhibition test, ToxiChromotest, MetPLATE, and three different modifications of a luminescent bacterial test), enzyme inhibition (reverse electron transport), plants (duckweed growth inhibition and red clover seed germination), and soil animals (Folsomia candida, Enchytraeus albidus, and Enchytraeus sp.). The luminescent bacterial tests were used as prescreening tests. Chemical analyses of samples were carried out simultaneously. Both toxicity and oil concentration, including those of polyaromatic hydrocarbons (PAHs), were reduced during composting and soil quality improved significantly. The total oil hydrocarbon concentration decreased from 90,000 to 19,000 mg/kg, measured with the IR method, in 4 months, and from 86,000 to 1400 mg/kg, measured with GC method. The concentration of PAHs decreased from 135 to 23.5 mg/kg. During the fourth month of composting (stabilization stage), the proportion of the heaviest oil fractions (asphaltenes) became dominant. Toxicity varied between different samples and between different bioassays; however, the first sample was significantly more toxic than the others, and most of the tests revealed a decrease in toxicity during the composting process.

Temperature-time relationship in collembolan response to chemical exposure.

Effects of temperature on chemical toxicity to a collembolan, Folsomia candida, in relation to time were studied in this experiment. Field soil was used as a test substrate. Collembolans were incubated at three different temperatures (+13, +16, and +19 degrees C) and in two different dimethoate concentrations (1 and 3 mg/kg), clean soil serving as the control. Four destructive samplings were done at 2-week intervals. Dimethoate degradation was also analyzed. Dimethoate 1 mg/kg had a slight effect on both adult growth and reproduction, whereas 3 mg/kg was fatal to F. candida in the soil used. Toxic effects tended to last longer at low temperature than at high temperature, but the differences were not extensive. Temperature was negatively correlated with adult growth but positively correlated with reproduction. The dimethoate degradation rate was similar at all temperatures but differed with the concentration.

Effect of soil moisture on pesticide toxicity to an enchytraeid worm, Enchytraeus sp.

The aim of the study was to find out whether soil moisture affects toxicity of organic pesticides to an enchytraeid worm. Laboratory experiments were carried out with dimethoate and benomyl, using a small Enchytraeus sp. as the test species. Substrate was natural agricultural field soil cultivated without pesticides for several years. Experimental design consisted of three soil moistures (40, 55, and 70% of water holding capacity) and five pesticide concentrations, plus controls. Measured parameters were survival, size of the parent worms and number and size of juveniles produced. Dimethoate was relatively non-toxic to this species. Dimethoate did not decrease survival, but sublethal effects on adult size and number of juveniles were observed. Adverse conditions in dry soil masked these effects; dimethoate appeared to be less toxic in dry soil than in moist soil. Benomyl caused significant mortality and the effects were very abrupt. Toxicity of benomyl decreased with increasing soil moisture content; in moist soil the worms survived at higher benomyl concentrations than in drier soils.

Toxicity of dimethoate to some soil animal species in different soil types.

Toxicity of dimethoate (insecticide) to an earthworm (Aporrectodea caliginosa tuberculata), a collembola (Folsomia candida), and an enchytraeid worm (Enchytraeus crypticus/variatus) was studied in three different soil types (artificial soil, clayey soil, and humus sandy soil). Parameters measured were survival and biomass change of the earthworms and survival and reproduction of the collembolas and enchytraeids. The degradation of dimethoate was analyzed too. Toxic effects were observed at the concentrations of some mg/kg dry soil. The biomass reduction of the earthworms occurred at lower concentrations than reduction in survival. The collembolas were more susceptible to dimethoate than the enchytraeids. High organic matter content of the soil reduced the toxic effects. The degradation of dimethoate was rather slow in the soils and under conditions tested. Half-life varied between 41 and 84 days.