Bioavailability in soils

The consumption of locally-produced vegetables by humans may be an important exposure pathway for soil contaminants in many urban settings and for agricultural land use. Hence, prediction of metal and metalloid uptake by vegetables from contaminated soils is an important part of the Human Health Risk Assessment procedure. The behaviour of metals (cadmium, chromium, cobalt, copper, mercury, molybdenum, nickel, lead and zinc) and metalloids (arsenic, boron and selenium) in contaminated soils depends to a large extent on the intrinsic charge, valence and speciation of the contaminant ion, and soil properties such as pH, redox status and contents of clay and/or organic matter. However, chemistry and behaviour of the contaminant in soil alone cannot predict soil-to-plant transfer. Root uptake, root selectivity, ion interactions, rhizosphere processes, leaf uptake from the atmosphere, and plant partitioning are important processes that ultimately govern the accumulation ofmetals and metalloids in edible vegetable tissues. Mechanistic models to accurately describe all these processes have not yet been developed, let alone validated under field conditions. Hence, to estimate risks by vegetable consumption, empirical models have been used to correlate concentrations of metals and metalloids in contaminated soils, soil physico-chemical characteristics, and concentrations of elements in vegetable tissues. These models should only be used within the bounds of their calibration, and often need to be re-calibrated or validated using local soil and environmental conditions on a regional or site-specific basis.Mike J. McLaughlin, Erik Smolders, Fien Degryse, and Rene Rietr

The price of mobility

This paper addresses the question concerning the price of geographic mobility in various labour market and migration scenarios. Pivotal points are expected mobility premiums which are sufficient to tip the scales in favour of moving to a geographically distinct location. These premiums are first derived within a theoretical model, accounting not only for location-specific amenity levels or labour market conditions, but also for heterogeneous personality traits and preferences. Derived hypotheses demonstrate that—in presence of heterogeneous psychic costs or adjustment capabilities—expected mobility premiums can remain distinctly positive even in an unemployment scenario. Furthermore, adjustment capabilities are to a large extent related to earlier mobility experiences, implying that labour mobility is partially learnable

DISSOLVED ORGANIC-MATTER, CADMIUM, COPPER AND ZINC IN PIG SLURRY-SIZE AND SOIL SOLUTION-SIZE EXCLUSION CHROMATOGRAPHY FRACTIONS

Sephadex size exclusion chromatography was used to prepare molecular size fractions from liquid pig slurry, before and after aerobic interaction with a loamy-sand soil. In the liquid fractions organic matter was characterized and some components were identified.The distribution of zinc and copper over MW-classes was determined. In pig slurry-liquid one third of the copper and zinc was found in the mass range &gt; 50,000. After 3 days contact with soil, copper concentration increased and 10 % was found in the nominal molecular mass range 50,000. The zinc concentration did not change, but the MW distribution had shifted in favor of higher molecular masses.Cation exchange experiments (4 hours) with the above fractions showed a zinc exchange rate of 50 % per hour, typically. Copper complexes in HMW-fractions did not exchange, which was tentatively explained by the measured high thermodynamic complex stability. Copper pig slurry-liquid LMW-fractions showed an exchange rate of 25 % per hour; the reaction stopped when 50 % was left, indicating the presence of stable LMW copper species. After incubation with soil the LMW copper showed a constant dissociation rate of 20 % per hour.</p