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Biomedical subjects

M Baskaran

Publications and source records attributed to M Baskaran.

24 records · Page 2Linked to original sources
PubMed2001

Scavenging of thorium isotopes in the Arctic regions: implications for the fate of particle-reactive pollutants.

The sources of inorganic pollutants to the Arctic areas are reviewed using previously published results. The removal of particle-reactive pollutants is discussed using thorium scavenging as an analog. The scavenging of 234Th from the upper water column (approximately 100 m) and sediment inventory of 230Th from the deep Arctic waters is compared to different ocean basins in the subarctic areas. Such a comparison shows that 234Th is in equilibrium with its parent, 238U, in certain regions of the Canada Basin of the Arctic Ocean, while it is deficient in other regions of the arctic as well as in sub-polar ocean basins. This implies that the particle-reactive pollutants in the deep Arctic of the Canada Basin are less likely to be removed from the deep waters and will eventually be transported out of this area. We have utilized the 230Th inventory in sediments from the Arctic area to determine the removal rates of particle-reactive nuclides. The 230Th inventory in the deep Arctic Ocean of the Canada Basin is much lower than the Norwegian Sea and the Fram Strait of the Arctic as well as all other sub-polar world oceans. These observations suggest that any pollutants into the deep Arctic areas of the Canada Basin are less likely to be removed locally and may be transported out of this area. In those areas, the colloidal material could potentially play a major role in the removal of particle-reactive contaminants.

Arctic Regions↗
PubMed2001

Organic carbon flow in the Ob, Yenisey Rivers and Kara Sea of the Arctic region.

Stable carbon isotope and elemental C/N ratios of the organic fraction of a set of samples along a transect in the Ob and Yenisey Rivers into the Kara Sea in the Arctic were measured. Previously, the concentrations of 239,240Pu and 137Cs in these same samples had been determined. The coupled measurements were carried out to assess possible connectivity between organic carbon flow into the Kara Sea and transport of radioactive nuclides in this marine environment. Organic carbon flow into the Kara Sea is influenced significantly by terrigenous sources carried by the Ob and Yenisey Rivers. The carbon isotope-organic carbon relationship provides evidence that a rich source of terrigenous carbon exists in the riverine system. A weak, but significant relationship between stable carbon isotope ratio and 137Cs suggests that most of the 137Cs is derived from riverine particles, as compared to Pu which is also derived from in situ scavenging within the water column.

Arctic Regions↗
PubMed2001

Historical contamination of PAHs, PCBs, DDTs, and heavy metals in Mississippi River Delta, Galveston Bay and Tampa Bay sediment cores.

Profiles of trace contaminant concentrations in sediment columns can be a natural archive from which pollutant inputs into coastal areas can be reconstructed. Reconstruction of historical inputs of anthropogenic chemicals is important for improving management strategies and evaluating the success of recent pollution controls measures. Here we report a reconstruction of historical contamination into three coastal sites along the US Gulf Coast: Mississippi River Delta, Galveston Bay and Tampa Bay. Within the watersheds of these areas are extensive agricultural lands as well as more than 50% of the chemical and refinery capacity of the USA. Despite this pollution potential, relatively low concentrations of trace metals and trace organic contaminants were found in one core from each of the three sites. Concentrations and fluxes of most trace metals found in surface sediments at these three sites, when normalized to Al, are typical for uncontaminated Gulf Coast sediments. Hydrophobic trace organic contaminants that are anthropogenic (polycyclic aromatic hydrocarbons, DDTs, and polychlorinated biphenyls) are found in sediments from all locations. The presence in surface sediments from the Mississippi River Delta of low level trace contaminants such as DDTs, which were banned in the early 1970's, indicate that they are still washed out from cultivated soils. It appears that the DDTs profile in that sediment core was produced by a combination of erosion processes of riverine and other sedimentary deposits during floods. Most of the pollutant profiles indicate that present-day conditions have improved from the more contaminated conditions in the 1950-1970's, before the advent of the Clean Water Act.

Agriculture↗
PubMed1999

Sedimentary fluxes of 90Sr, 137Cs, 239,240Pu and 210Pb in the East Sea (Sea of Japan).

Sediment cores collected from the deep basins of the East Sea (Sea of Japan) provide an ongoing and historical record of artificial radionuclides contamination into one of the most highly publicized radioactive waste dumping areas in the world ocean. The depth distributions of 90Sr, 137Cs and 239,240Pu in sediment cores were investigated with the aid of 210Pb-derived sediment accumulation and mixing rates in the deep basins of the East Sea (Sea of Japan). Five box core samples were collected from the northern Yamato Ridge, Korea Plateau, Ulleung and Japan Basins below 1000-m depth. Sediment inventories of 137Cs and 239,240Pu are inversely correlated with water depth and linearly correlated with sediment accumulation rates. The inventories of these nuclides are linearly correlated with the accumulation rates of organic carbon in sediments. The 238Pu/239,240Pu activity ratios in sediments are 0.036 +/- 0.009 suggesting that most of the Pu to the study area is derived from the global fallout. The activity ratios of 239,240Pu/137Cs, and 90Sr/137Cs in bottom sediments are much lower than those of global fallout due to the differences of particle affinity and biological uptake of these nuclides. Sediment inventories of 90Sr and 137Cs constitute < 4% of the anticipated inventories from the global fallout, while those of 239,240Pu constitute 30-150% of the anticipated inventories from the global fallout. The residence time of the dissolved 239,240Pu in the study area is estimated to be 200-400 years based on the sediment inventory and/or sediment accumulation rate, and water column inventory.

Cesium↗
PubMed1995

Distribution of 239,240Pu and 238Pu concentrations in sediments from the Ob and Yenisey Rivers and the Kara Sea.

The major sources of plutonium isotopes in the environment are from nuclear weapons testing via global and close-in (debris) fallout, nuclear fuel reprocessing and fabrication plant effluents. Measurements of differences in the Pu isotopic ratios (239Pu/240Pu, 238Pu/239,240Pu and 241Pu/239,240Pu) have yielded information not only on the time horizons for sedimentary deposits but also on the sources of Pu. We have measured 238Pu, 239,240Pu and 137Cs concentrations in the surficial sediments of the Ob and Yenisey Rivers (Russia) and the Kara Sea. The downcore variations of 238Pu and 239,240Pu concentrations have also been measured in some sediment cores. A comparison of the sediment core inventories of 239,240Pu along with the 238Pu/239,240Pu activity ratios with those expected from global fallout at the study sites allows us to estimate the relative amounts of reactor-derived 238Pu and 239,240Pu from the dumped reactor sites in the study area. In surficial sediment samples, the 239,240Pu concentrations vary between 9.4 and 627 mBq kg-1, with a mean of 250 mBq kg-1. The 238Pu/239,240Pu activity ratios vary between 0.009 and 0.065 with an average value of 0.034 +/- 0.003. This range can be compared to the average 238Pu/239,240Pu activity ratio of 0.030 for the year 1993 from nuclear weapons testing and SNAP fallout obtained from soil studies, indicating very little additional sources of 238Pu to the sediments in the study area. In sediment cores, the maximum depths at which 239,240Pu was detected varied between 6 and 12 cm. These depths yield average apparent sedimentation rates in the coastal Kara Sea between 1.5 and 3.0 mm yr-1 (assuming Pu input since 1952, and no sediment mixing).

Arctic Regions↗