Toxic substance, degradation

Combustion in an incinerator is the only practical way to deal with many waste streams.This is particularly true of solid and concentrated wastes and toxic wastes such as those containing halogenated hydrocarbons, pesticides, herbicides, etc. Many of the toxic substances encountered resist biological degradation and persist in the natural environment for a long period of time. Unless they are in dilute aqueous solution, the most effective treatment is usually incineration. 

During decomposition of plant remains, many phenolic compounds are released by leaching, microbial degradation or are synthesized by microbial activity. In forestry, problems of natural regeneration and reforestation are connected to the presence of phenolic substances deposited in the soil. Methods for extrachon and identification of toxic substances from different soil types (mineral or organic) are described. The method for extracting of soil phytotoxins is based on the use of ethylacetate and methanol (free phenolics) and alkaline hydrolysis (bound phenolics). 

Laboratory analysis of site soils should be made to determine the presence and population density of naturally occurring microbes that are capable of degrading the contaminant. At a minimum, these analyses should include plate counts to determine the relative number of microbes of several types, the substrate (food) type that reflects the type of chemicals they are likely to consume, and if toxic substances are present. 

Waste products from the degradation of organic substances in animal metabolism include carbon dioxide (CO2), water (H2O), and ammonia (NH3). In mammals, the toxic substance ammonia is incorporated into urea and excreted in this form (see p. 182). 

Once inside the body, extremely hydrophilic compounds tend to be excreted more readily by the kidney. That could be useful, because it lowers toxicity. Additionally, chemical classes and functional groups known to be toxic—as well as those that can be bioactivated into toxic substances—should be avoided when designing chemical products. Chemicals can also be designed to shield active toxic sites or to facilitate metabolic degradation to nontoxic metabolites. 

A number of major studies to analyze triazine herbicides and their degradation products (i.e., metabolites) in water have been carried out by the United States Geological Survey (USGS), Water Resources Division, in the Toxic Substances Hydrology Program. These studies investigated four major water resources - groundwater, surface water, reservoirs, and precipitation. 

Metabolic processes of fungi, bacteria, and protozoa act to degrade toxic substances in the water and soil environments. 

Steen, W.C., Paris, D.F., Baughman, G.L. (1979) Effects of sediment sorption on microbial degradation of toxic substances, in Proc. 

Steen, W.C., Paris, D.F., Baughman, G.L. (1982) Effects of sediment sorption on microbial degradation of toxic substances. In Contaminants and Sediments Fate and Transport, Case Studies, Modeling, Toxicity. Vol. 1, Baker, R.A., Editor, p. 477, Ann Arbor Science, Ann Arbor, Michigan. 

Soil. DT50 c. 10 days Degraded by hydrolysis and debromination to less toxic substance such as hydrobenzoic acid... 

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