Leaching of toxicants

The pH of rainwater is normally about 6 but can be reduced significantly by absorption of acidic exhaust gases from power stations, industrial combustion or other processes, and vehicles. Acids may also enter the waterways as a component of industrial effluent. In addition to the direct adverse effects on aquatic systems (Table 16.12) low pH can result in the leaching of toxic metals from land, etc. 

The higher content of DDT metabolites (DDE + DDD) compared with DDT itself (i.e., (DDE + DDD)/DDT > 1) in surface waters indicates a high degree of microbial transformation of the initial compound in the soil. The DDE and DDD are formed by DDT dehydrochlorination and dechlorination, respectively. On the whole it means that loss or leaching of toxic compounds take place from RPA formed some decades ago. 

Prevents future acid generation and leaching of toxic heavy metals. 

Orem W. H., Feder G. L., and Finkelman R. B. (1999) A possible link between Balkan Endemic Nephropathy and the leaching of toxic organic compounds from Pliocene lignites by groundwater. Int. J. Coal Geol. 40, 237—252. 

The types of test chambers used in toxicity tests depend on the test species. Various sizes of beakers, aquaria, jars, bowls, and petri dishes have been used. The test chambers usually are constructed of material such as glass. Teflon, and certain plastics that minimize leaching of toxicants and adsorption of the test substance. 

The first phase of the Bureau s research [1 ] showed that phosphogypsum was not corrosive by Environmental Protection Agency (EPA) criteria. The study also presented evidence that phosphogypsum would not be toxic by EPA criteria and that trace elements and radium would not be leached from the stockpiles. These conclusions were obtained from statistical analyses of extensive quantities of spectrographic and radiological data. More direct confirmation of these conclusions was needed to decisively answer the question of leaching of toxic elements and radium from phosphogypsum stockpiles. 

Finding 5-2. The Russian two-stage neutralization/ bitumenization process generates a large amount of secondary wastes that in the United States would require being land-filled and monitored indefinitely. The lack of information on the long-term stability of these wastes and the leaching of toxic materials from them (see Secondary Waste Issues ) is a cause for concern. 

Aqueous extracts. Various bioassay protocols are available for testing soil elutriates or leachates. Historically these have previously been available for aquatic tests. However, it may be inappropriate to project effects generated with aquatic species to soil organisms or ecosystems. With the development of whole soil bioassays, the use of elutriate or leachate tests focuses now on the prediction of threats to groundwater (leaching of toxicants) or surface water (contaminant run-off). Tests using aqueous extracts address pollutants soluble in water, and therefore are a measure of mobile toxicants. 

Francis CW, White GH. 1987. Leaching of toxic metals from incinerator ashes. J Water Pollut Control Fed 59 979-986. 

Packham, R. F. (1971), The leaching of toxic stabilisers from unplasticised PVC water pipe Parts I-III, Water treatment and examination 20, 108-164. 

The leaching of toxic species from a deposit of waste will also be affected by waste-related and environmental physico-chemical processes. Some layers of waste may be hydrophobic or impenetrable to leachate and the material may remain in situ in a relatively undegraded state for many years. However, once toxic species are in solution, reaction with the environment can occur in a number of ways. 

The leaching of toxic metal ions into groundwater by acid rain may also increase groundwater pollution. 

To date, the major adverse effects of acid rain include damage to lakes, streams, and forests degradation of soils leaching of toxic metals in the environment damage to man-made materials adverse respiratory effects in humans and degradation of air quality. It is very difficult to predict the future effects of acid rain on something as complex as an entire ecosystem. We do not know whether most of the effects that will occur have already taken place, or whether we have only seen the tip of the "acid iceberg" to come. 

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