Variability of Mercury Concentrations in Soil and Leaves of Acer plantanoides and Tilia platyphyllos in Poznań City,Poland

The paper presents the results of research on mercury in the soil and leaves of maple (Acer plantanoides) and linden (Tilia platyphyllos) collected in the four districts of the city of Poznań (Poland), which differ in terms of anthropogenic pressure. The average concentration of mercury in soil was 132 μg kg^?1. The highest concentration of mercury was determined in Tilia platyphyllos (233 μg kg^?1), whereas in Acer plantanoides it amounted to 207 μg kg^?1. Based on the study, it was found that the highest concentration of mercury in the investigated leaf species was observed in the samples collected in the districts of Grunwald, Je?yce, and Old Town. The lowest concentration was observed in the samples collected in the district of New Town. The comparison of the obtained results of mercury concentration in soil and leaf samples was made in terms of anthropogenic pressure in the investigated areas and depending on the studied leaf species. Based on the statistical analysis, it was found that there is no statistically significant relationship between mercury concentration in both studied species of trees. There was, however, a relationship between the mercury concentration in leaves and soil.     

Restoration of effectiveness of R. meliloti ineffective mutants by transduction of high level streptomycin resistance.

Rhizobium meliloti lysine dependent mutant, L5-30lys, was ineffective and this mutation was not cotransducible to lys. Transduction of chloramphenicol and linked temperature sensitive mutations did not change its symbiotic properties. Subsequent transduction of high level streptomycin resistance restored its effectiveness. Streptomycin resistance marker was linked to chloramphenicol resistance and temperature sensitive markers.     

Toward a Typology of Dynamic and Hazardous Work Environments

The most hazardous work environments share one feature in common: constant change. Many different, but constantly changing hazards are found in agriculture, construction, mining, and transport. This dynamic feature of workplace hazards varies by: (1) degree of control, (2) predictability, (3) visibility, (4) movement, and (5) degree of speed and force. In some cases the actions of the dynamic hazards are required for production to take place, and in many cases, several different hazards may overlap and interact. Finally, whether intentional or unintentional, some dynamic hazards are human generated. These are some of the features that distinguish dynamic and hazardous work environments across a variety of industries. The authors propose a preliminary typology of dynamic and hazardous work environments, along with a schema to systematically observe the dynamic characteristics of these hazards. The implications of this typology are considered with respect to worker training, hazard awareness, and safe work practices. For example, the implementation of the Hierarchy of Control is shown to require active worker involvement at every level in the hierarchy, except where an environmental hazard has been completely eliminated.