PCBs, PBDEs and pesticides released to the Arctic Ocean by the Russian rivers Ob and Yenisei

The Ob and Yenisei Rivers contribute 37% of riverine freshwater inputs to the Arctic Basin and thus represent an important pathway for the land-Arctic ocean exchange of contaminants. Sampling was carried out in the Yenisei (2003) and Ob (2005) River estuaries and Kara Sea to address the general lack of reliable dissolved contaminant flux data for these major rivers. Contaminant analyses were performed by high resolution mass spectrometry on sample extracts taken from filtered large volume water samples (50-100 L) and concentrated in situ onto XAD-2 resin columns. Hexachlorocyclohexanes (HCHs), the polychlorinated biphenyl (PCB) mixtures Sovol and trichlorodiphenyl, dichlorodiphenyltrichloroethane (DDT), as well as "penta" brominated technical mixtures of polybrominated diphenyl ethers (PBDEs) are important contributors to persistent organohalogen contamination for these waterways. Dissolved fluxes to the Kara Sea were estimated at sigmaHCH 246 kg/yr, sigmaPCB 63 kg/yr, sigmaDDT 16 kg/yr, hexachlorobenzene 8 kg/yr, alpha-endosulfan 8 kg/ yr, dieldrin 5 kg/yr, sigmaPBDE 4 kg/yr, and chlordanes 4 kg/yr. Contaminant fluxes from these rivers are similar to those reported for major Canadian rivers, confirming expectations that the Ob and Yenisei are also major point sources for the Arctic basin.     

The effect of cultivation on structure in soils affected by opencast mining for coal

Two grassland sites, reinstated after opencast mining for coal, were used to assess the effect of cultivation on structure rehabilitation. In general, cultivation had an adverse effect over a range of porosity and aggregate stability indices. This effect tended to be more marked in macro- rather than micro-aggregate stability, in the upper rather than the lower half of the tillage layer and at higher intensities of cultivation. Some tillage responses persisted after two years. Cultivation effects were partly explained by mixing of soil within the tilled layer. However, results indicated some direct physical destruction of aggregates and a large reduction in aggregate stability. Data available did not point to any clear cause of this reduction in stability. Nevertheless, there was some evidence that cultivation may have disrupted the stabilisation of aggregates by organic matter, without influencing overall organic content. Net structural responses to cultivation are a balance of adverse and beneficial effects. In replaced soils this balance is negative. For this reason, tillage should be restricted where structure rehabilitation is a priority.