Losses from leaching

How much does Nitrogen Fertilizer Contribute to Nitrate Leaching when Winter Wheat is Growiii We saw earlier that direct nitrate losses from nitrogen fertilizer given to winter wheat are often relatively small. We saw too that... 

The last reaction cited above as shown is very effectively catalyzed by bacterial action but is very slow chemically by recycling the spent ferrous liquors and regenerating ferric iron bacterially, the amount of iron which must be derived from pyrite oxidation is limited to that needed to make up losses from the system, principally in the uranium product stream. This is important if the slow step in the overall process is the oxidation of pyrite. The situation is different in the case of bacterial leaching of copper sulfides where all the sulfide must be attacked to obtain copper with a high efficiency. A fourth reaction which may occur is the hydrolysis of ferric sulfate in solution, thus regenerating more sulfuric acid the ferrous-ferric oxidation consumes acid. 

Mlrex. Mirex does not leach into the soil profile and is predicted to volatilize only slowly. There Is no evidence for any rapid transformation so it should be considered persistent. Because It is so strongly adsorbed to the soil and stays on the surface, a major loss from terrestrial systems would probably be erosion and transport Into surface waters. 

The saturated hydrocarbon moieties give lipids an aliphatic character, and thus hydro-phobic properties, which limit their loss from artefacts by water leaching. However, they are subject to chemical and microbiological alterations since they have a limited number of reactive sites, they are relatively less susceptible to structural modification and degradation than polysaccharides, proteins and nucleotides. 

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. 

The detection of DDT in surface waters as (DDE + DDD)/DDT < 1 reflects minor transformation of the initial insecticide in the soil and hence the toxicants loss or leaching from recently formed RPA or so-called local pedogeochemical anomalies, LPA (former action zone of plants for DDT preparations production places of accidental spillage or output of the preparations areas of storage or burial—tombs, etc. that are characterized by extremely high contamination level (Lunev, 1997 Silowiecki et al., 1998). 

Meanwhile, the detection of a- ory-isomer HCH in relatively high concentrations when compared with other isomers suggest relatively little transformation of HCH or lindane, which are known to include up to 70% of ct-isomer and no less than 99% of y-isomer, respectively. On the whole this would suggest a loss or leaching from recently formed RPA or LPA. 

HCH insecticide in agricultural areas of the Mugano-Salyansk land region and also loss or leaching of its residues from recently formed RPA (Galiulin and Galiulina, 1996). Meanwhile the proportion of DDT in the bottom sediments of rivers was DDE + DDD/DDT < 1, that may indicate a relatively little transformation of this insecticide in the present environment (Galiulin, 1994). 

Thus the application of the conceptual model to monitoring data shows an existence of the ecological risk of river waters entering in the Caspian Sea. This is connected with (a) loss or leaching of DDT and HCH residues with relatively low transformation from LPA, (b) possible secondary risk of water contamination by POCs desorbed from bottom sediments, and (c) POCs content in aquatic ecosystems at toxic concentrations for the most sensitive organisms. 

Thus, at present, the input of unused DDT and HCH insecticides in water and bottom sediments of the rivers and reservoirs of the Caspian Sea basin is mainly connected with loss or leaching from old RPA or young LPA. As regards PCBs, their input is mainly related to industrial sources. The high toxicity of POCs for organisms and their persistence in the water and sediments are the principal forms of ecological risk for rivers and the Caspian Sea. The behavior of POCs in the northern part of... 

EFRC (1992). Assessment of nitrate leaching losses from organic farms. Einal report for the Ministry of Agriculture, fisheries and Eood. Contract CSA 2248. Elm Farm Research Centre Hamstead Marshall. 

Taking all these factors into account, overall leaching losses from organic farms tend to be... 

Davis-Carter, J.G. and B. Burgoa (1993). Atrazine runoff and leaching losses from soil in tilted beds as influenced by three rates of lagoon effluent. J. Environ. Sci. Health B, 28 1-18. 

Root samples must be washed to reduce contamination, but even so complete clean up is impossible for many soil types. Sometimes a brief period of ultrasonic treatment is used in a water bath. Reliable studies of leaching losses from plant roots are scarce because they are so difficult to conduct, and the results are rarely unequivocal. 

The N-serve literature points out that a nitrification inhibitor is helpful only when conditions favor high nitrogen loss from the soil. Such conditions are heavy rainfall or heavy irrigation, coarse-textured soil, and soil in the pH range where nitrification readily occurs. Nitrate thus formed will leach down into anaerobic soil layers. 

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