The transport of antibiotic resistant Escherichia coli through several soils was evaluated. Up to 96% of the bacteria irrigated onto the surface of 280 mm deep intact columns were recovered in the effluent. Soil structure appeared to be related to the extent of transport. Columns prepared from mixed, repacked soil were much more effective bacterial filters than the intact soils. As rate of water input increased, the fraction of E. coli recovered in the effluent increased. The observed behavior of E. coli and the Cl− solution in which they were suspended suggests that flow through soil macropores, which bypasses the adsorptive or retentive capacities of the soil matrix, is a common phenomenon. In waste disposal systems dependent on purification in the soil profile, this could significantly increase the probability of groundwater contamination.

In areas that remain unaffected by industrial pollution soil acidification is mainly caused by the release of protons (H ÷) during the oxidation of carbon (C), sulphur (S) and nitrogen (N) compounds in soils. In this review the processes of H ÷ ions release during N cycling and its effect on soil acidification are examined. The major processes leading to acidification during N cycling in soils are: (i) the imbalance of cation over anion uptake in the rhizosphere of plants either actively fixing N 2 gas or taking up NH 4 ions as the major source of N, (ii) the net nitrification of N derived from fixation or from NH 4 and R -N H 2 based fertilizers, and (iii) the removal of plant and animal products containing N derived from the process described in (i) and losses of NO3-N by leaching when the N input form is N2, NH 4 or R -N H 2. The uptake of excess cations over anions by plants results in the acidification of the rhizosphere which is a "localized" effect and can be balanced by the release of hydroxyl ( O H -) ions during subsequent plant decomposition. Nitrification of fixed N 2 or NH 4 and R -N H 2 based fertilizers, and loss of N from the soil either by removal of products or by leaching of NOa-N with a companion basic cation, lead to 'permanent' acidification.

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Considerable data of a physical-chemical nature form the fundamentals upon which the development of liquid-liquid extraction processes may be based. Among these data are the solubility relations-mutual solubility and distribution coefficients-for the constituents involved. These relations cannot yet be predicted but must be obtained experimentally.The usual extraction system involves three liquid components-one pair of immiscible liquids and two pairs of miscible liquids. When the three components are present in such quantities that two liquid phases exist, the common miscible liquid distributes itself between the immiscible pi ir in accordance with the distribution law. The presence of the miscible liquid increases the solubilities