John E. Pinder

Atmospheric deposition, resuspension, and root uptake of Pu in corn and other grain-producing agroecosystems near a nuclear fuel facility.

Plutonium released to the environment may contribute to dose to humans through inhalation or ingestion of contaminated foodstuffs. Plutonium contamination of agricultural plants may result from interception and retention of atmospheric deposition, resuspension of Pu-bearing soil particles to plant surfaces, and root uptake. Plutonium on vegetation surfaces may be transferred to grain surfaces during mechanical harvesting. Data obtained from corn grown near the U.S. Department of Energys H-Area nuclear fuel chemical separations facility on the Savannah River Site were used to estimate parameters of a simple model of Pu transport in agroecosystems. The parameter estimates for corn were compared to those previously obtained for wheat and soybeans. Despite some differences in parameter estimates among crops, the relative importances of atmospheric deposition, resuspension, and root uptake were similar among crops. For even small deposition rates, the relative importances of processes for Pu contamination of corn grain should be: transfer of atmospheric deposition from vegetation surfaces to grain surfaces during combining greater than resuspension of soil to grain surfaces greater than root uptake. Approximately 3.9 X 10(-5) of a years atmospheric deposition is transferred to grain. Approximately 6.2 X 10(-9) of the Pu inventory in the soil is resuspended to corn grain, and a further 7.3 X 10(-10) of the soil Pu inventory is absorbed and translocated to grains.

Insect Herbivory and Photosynthetic Pathways in Old-Field Ecosystems

Three old-field communities of varying composition near Aiken, South Carolina, were used to test the hypothesis that phytophagous insects avoid consuming plants possessing the C/sub 4/ photosynthetic pathway and consume plants that possess only the C/sub 3/ pathway. The relative abundances of stable carbon isotopes in insect tissues, which indicate consumption of C/sub 3/ or C/sub 4/ plants, were used to determine if insects were consuming C/sub 3/ and C/sub 4/ plants in proportion to their abundance in the plant community. In one community, the carbon isotope ratio for insects was significantly less than that expected for proportional consumption and indicated avoidance of C/sub 4/ species. Insect consumption of C/sub 4/ plants was approx. = 50% of that expected if insects were consuming C/sub 3/ and C/sub 4/ plants in proportion to their abundance. In the other two communities, the differences between observed and expected isotopic ratios were not significant. Levels of insect consumption of C/sub 4/ plants in these two communities were, respectively, approx. = 82% and approx. = 126% of those expected for proportional consumption. The results suggest that the degree of avoidance varies among plant communities.

Food chains and biogeochemical pathways: contributions of fallout and other radiotracers.

This paper reviews examples of how measurements of global fallout in the environment and related tracer radionuclides have been used to enhance our basic knowledge of biogeochemical processes and food-chain pathways. Because it is these fundamental, natural processes that control the transport and accumulation of such trace substances in the environment, direct measurements of trace substances over time and space reveal strong insights into these processes. The necessity to monitor global fallout transport, although largely motivated by human health concerns, gave rise to a plethora of new information about plants, animals, and natural and agricultural ecosystems and how they function. This review provides a small selection of examples in the areas of plant and animal physiology, productivity and energy transfer in food chains, biogeochemical cycles of certain elements and their analogues, feeding relationships and movements of organisms, and the agriculture-based human food chain. It is concluded that if society is to cope successfully with continued growth of the human population and resource consumption, more knowledge is still required about these fundamental processes. The use of radiotracers can contribute greatly to this need, but current funding priorities, societal attitudes, and onerous regulations on the use of radioactivity may continue to limit such applications.

The interrelationships among plant biomass, plant surface area and the interception of particulate deposition by grasses.

The interrelationships among plant biomass, plant surface area and interception fraction were determined for the interception by corn of 238Pu-bearing particles released to the atmosphere from the H-Area nuclear fuels chemical separations facility on the U.S. Department of Energys Savannah River Plant in Barnwell County, South Carolina. The relationship between interception fraction and corn biomass was accurately approximated by a filtration model with an absorption coefficient of 3.60 m2 kg-1. A filtration model with an absorption coefficient of 2.91 m2 kg-1 accurately approximated the relationship between biomass and interception fraction for data compiled from the literature for a variety of grass species. A linear regression model accurately approximated the relationship between interception fraction and surface area, but was not a better predictor of interception fraction than the filtration model for biomass.

Cesium accumulation by fish following acute input to lakes: a comparison of experimental and Chernobyl-impacted systems.

An uptake parameter u (Lkg(-1)d(-1)) and a loss rate parameter k (d(-1)) were estimated for the patterns of accumulation and loss of (133)Cs by three fish species following an experimental (133)Cs addition into a pond in South Carolina, USA. These u and k parameters were compared to similar estimates for fish from other experimental ponds and from lakes that received (137)Cs deposition from Chernobyl. Estimates of u from ponds and lakes declined with increasing potassium concentrations in the water column. Although loss rates were greater in the experimental ponds, the times required to reach maximum Cs concentrations in fish were similar between ponds and lakes, because ponds and lakes had similar retentions of Cs in the water column. The maximum Cs concentrations in fish were largely determined by initial Cs concentrations in the water column. These maximum concentrations in fish and the times required to reach these maxima are potentially useful indicators for assessments of risks to humans from fish consumption.

Cesium accumulation by aquatic organisms at different trophic levels following an experimental release into a small reservoir

The rates of accumulation and subsequent loss of stable cesium (¹³³Cs) by organisms at different trophic levels within plankton-based and periphyton-based food chains were measured following the addition of ¹³³Cs into a small reservoir near Aiken, South Carolina, USA. An uptake parameter u (L kg⁻¹ d⁻¹ dry mass) and a loss rate parameter k (d⁻¹) were estimated for each organism using time-series measurements of ¹³³Cs concentrations in water and biota, and these parameters were used to estimate maximum concentrations, times to maximum concentrations, and concentration ratios (C(r)). The maximum ¹³³Cs concentrations for plankton, periphyton, the insect larva Chaoborus punctipennis, which feeds on plankton, and the snail Helisoma trivolvis, which feeds on periphyton, occurred within the first 14 days following the addition, whereas the maximum concentrations for the fish species Lepomis macrochirus and Micropterus salmoides occurred after 170 days. The C(r) based on dry mass for plankton and C. punctipennis were 1220 L kg⁻¹ and 5570 L kg⁻¹, respectively, and were less than the C(r) of 8630 L kg⁻¹ for periphyton and 47,700 L kg⁻¹ for H. trivolvis. Although the C(r) differed between plankton-based and periphyton-based food chains, they displayed similar levels of biomagnification. Biomagnification was also indicated for fish where the C(r) for the mostly nonpiscivorous L. macrochirus of 22,600 L kg⁻¹ was three times less than that for mostly piscivorous M. salmoides of 71,500 L kg⁻¹. Although the C(r) for M. salmoides was greater than those for periphyton and H. trivolvis, the maximum ¹³³Cs concentrations for periphyton and H. trivolvis were greater than that for M. salmoides.

The interception and retention of 238Pu deposition by orange trees.

Radioisotope thermoelectric generators (RTG) transform the heat produced during the alpha decay of 238Pu into electrical energy for use by deep-space probes, such as the Voyager spacecraft, which have returned images and other data from Jupiter, Saturn and Uranus. Future missions involving RTGs may be launched aboard the space shuttle, and there is a remote possibility that an explosion of liquid-hydrogen and liquid-oxygen fuel could rupture the RTGs and disperse 238Pu into the atmosphere over central Florida. Research was performed to determine the potential transport to man of atmospherically dispersed Pu via contaminated orange fruits. The results indicate that the major contamination of oranges would result from the interception and retention of 238Pu deposition by fruits. The resulting surface contamination could enter human food chains through transfer to internal tissues during peeling or in the reconstituted juices and flavorings made from orange skins. The interception of 238Pu deposition by fruits is especially important because the results indicate no measurable loss of Pu from fruit surfaces through time or with washing. Approximately 1% of the 238Pu deposited onto an orange grove would be harvested in the year following deposition.

The annual cycle of plutonium in the water column of a warm, monomictic reservoir

Abstract An annual cycle occurs in the 239,240 Pu inventories of the water column of Pond B, an 87-ha warm monomictic reservoir on the US Department of Energys Savannah River Site in Barnwell Co., South Carolina. The pond has elevated concentrations of 238 Pu and 239,240 Pu in sediments due to releases from former reactor operations and continues to receive additional Pu input from atmospheric deposition. The 239,240 Pu inventories in the water column display annual cycles that differ between surface waters (i.e. 0–6 m deep) and deeper waters ( i . e . > 6 m deep ) that are anoxic in summer months. For surface waters, the 239,240 Pu inventory increases following turnover in November to a maximum in March followed by a decline until later summer when minimum inventories occur. For deeper waters, the 239,240 Pu inventories increase rapidly following turnover and reach maximum values in March. The inventories in deeper waters remain large from March until turnover. Maximum inventories for the entire water column occur in March with minimum inventories at turnover in October and November. Turnover results in a redistribution of Pu across water depth but no measurable Pu loss from the water column. Ratios of 238 Pu: 239,240 Pu indicate that the cycle involves primarily Pu from sediment sources with little influence from atmospheric sources. Thus, the cycle represents net remobilization of 239,240 Pu from the sediments to the water column during the oxic, holomictic portion of the year followed by a net loss of Pu from the water column once stratification occurs.

Colonization of a Volcanic Mudflow by an Upper Montane Coniferous Forest at Lassen Volcanic National Park, California

Abstract Colonization of a relatively undisturbed 1915 debris flow by an upper montane coniferous forest was examined in Lassen Volcanic National Park in northern California in 1987. Seventy 100-m2 circular plots were arranged in four transects across the flow and sampled to measure tree densities, heights, basal areas and ages. The composition of the forest changed from a mixture of Abies magnifica, Pinus monticola and P. contorta on steep slopes to a forest dominated by P. contorta on shallow slopes. This pattern is typical for these terrains at the 2000-m elevations of the flow. Age data and historical photographs indicated little successful colonization before the late 1930s and peak colonization rates about 1955. Height growth has generally been slow with most trees being >20-y-old but <2-m tall; however, some individuals, including some recent colonizers, have shown rapid growth. This variation among individuals suggests (1) that the earliest colonizers are not necessarily those which will eventually dominate the forest and (2) that opportunities to invade and occupy the canopy may extend for 30 y after the first successful colonization.

Uptake of radiocesium from contaminated floodplain sediments by herbaceous plants.

Levels of radiocesium contamination in Sagittaria latifolia Willd. and Polygonurn punctutum Ell., two herbaceous plant species sampled from Steel Creek on the AEC Savannah River Plant, are not correlated with total radiocesium concentrations in the soils upon which they were growing. Soils showed a bimodal distribution of radiocesium contamination and were thus divided into low level and high level classes. With only one exception, plants from high and low level soils did not demonstrate significant differences in radiocesium contaminations. Concentration of radiocesium in leaves of Sagittaria latifolia was higher in plants growing on low level soils than on high level soils. Significant correlations were observed between radiocesium levels in component parts of the same plants; however, highest correlations occurred between similar components of near-neighbor plants of the same species. Uptake of radiocesium by these two species appears to be related to factors other than the total _ _ soil concentration of the isotopd.