Pollution and Oral Bioaccessibility of Pb in Soils of Villages and Cities with a Long Habitation History.

The Dutch cities Utrecht and Wijk bij Duurstede were founded by the Romans around 50 B.C. and the village Fijnaart and Graft-De Rijp around 1600 A.D. The soils of these villages are polluted with Pb (up to ~5000 mg/kg). Lead isotope ratios were used to trace the sources of Pb pollution in the urban soils. In ~75% of the urban soils the source of the Pb pollution was a mixture of glazed potsherd, sherds of glazed roof tiles, building remnants (Pb sheets), metal slag, Pb-based paint flakes and coal ashes. These anthropogenic Pb sources most likely entered the urban soils due to historical smelting activities, renovation and demolition of houses, disposal of coal ashes and raising and fertilization of land with city waste. Since many houses still contain Pb-based building materials, careless renovation or demolition can cause new or more extensive Pb pollution in urban soils. In ~25% of the studied urban topsoils, Pb isotope compositions suggest Pb pollution was caused by incinerator ash and/or gasoline Pb suggesting atmospheric deposition as the major source. The bioaccessible Pb fraction of 14 selected urban soils was determined with an in vitro test and varied from 16% to 82% of total Pb. The bioaccessibility appears related to the chemical composition and grain size of the primary Pb phases and pollution age. Risk assessment based on the in vitro test results imply that risk to children may be underestimated in ~90% of the studied sample sites (13 out of 14).

An ABC transporter and a TonB ortholog contribute to Helicobacter mustelae nickel and cobalt acquisition.

The genomes of Helicobacter species colonizing the mammalian gastric mucosa (like Helicobacter pylori) contain a large number of genes annotated as iron acquisition genes but only few nickel acquisition genes, which contrasts with the central position of nickel in the urease-mediated acid resistance of these gastric pathogens. In this study we have investigated the predicted iron and nickel acquisition systems of the ferret pathogen Helicobacter mustelae. The expression of the outer membrane protein-encoding frpB2 gene was iron and Fur repressed, whereas the expression of the ABC transporter genes fecD and ceuE was iron and Fur independent. The inactivation of the two tonB genes showed that TonB1 is required for heme utilization, whereas the absence of TonB2 only marginally affected iron-dependent growth but led to reduced cellular nickel content and urease activity. The inactivation of the fecD and ceuE ABC transporter genes did not affect iron levels but resulted in significantly reduced urease activity and cellular nickel content. Surprisingly, the inactivation of the nixA nickel transporter gene affected cellular nickel content and urease activity only when combined with the inactivation of other nickel acquisition genes, like fecD or ceuE. The FecDE ABC transporter is not specific for nickel, since an fecD mutant also showed reduced cellular cobalt levels and increased cobalt resistance. We conclude that the H. mustelae fecDE and ceuE genes encode an ABC transporter involved in nickel and cobalt acquisition, which works independently of the nickel transporter NixA, while TonB2 is required primarily for nickel acquisition, with TonB1 being required for heme utilization.

Effects of a drought period on physico-chemical surface water quality in a regional catchment area.

Hydrological drought periods are expected to become more severe in North-Western Europe as a result of climate change. This may have implications for water quality, as demonstrated by declining water quality of large rivers (e.g. Rhine, Meuse) during droughts. However, similar investigations in regional catchment areas are lacking to date. In the present study, we investigated the effects of a drought period on the water quality of the Dommel River, a tributary of the Meuse river in the Netherlands. Water quality during the drought of 2003 was compared to that in reference years (2004-2006) for 18 physical/chemical parameters using ANOVA analysis. It was demonstrated that the drought period of 2003 did not significantly affect water quality, although the origin of river flow during the drought shifted from mainly overland flow to deep groundwater flow and (treated) communal effluents. Significant differences in water quality were noted for some monitoring stations during the study period, which could be related to operational water management such as cleaning of sediment traps in the river and improvements in communal effluent treatment. The results of this study are interesting to water managers in Western Europe as they contribute to understanding the potential impact of climate change on water quality/quantity patterns in regional water systems.

Influence of hydropower dams on the composition of the suspended and riverbank sediments in the Danube.

Large hydropower dams have major impacts on flow regime, sediment transport and the characteristics of water and sediment in downstream rivers. The Gabcikovo and Iron Gate dams divide the studied Danube transect (rkm 1895-795) into three parts. In the Gabcikovo Reservoir (length of 40km) only a part of the incoming suspended sediments were deposited. Contrary to this, in the much larger Iron Gate backwater zone and reservoir (length of 310km) all riverine suspended sediments were deposited within the reservoir. Subsequently, suspended sediments were transported by tributaries into the Iron Gate backwater zone. Here they were modified by fractional sedimentation before they transgressed downstream via the dams. Compared with undammed Danube sections, Iron Gate reservoir sediment and suspended matter showed higher clay contents and different K/Ga and Metal/Ga ratios. These findings emphasize the importance of reservoir-river sediment-fractionation.