Effects of landfill gas on subtropical woody plants

An account is given of the influence of landfill gas on tree growth in the field at Gin Drinkers' Bay (GDB) landfill, Hong Kong, and in the laboratory. Ten species (Acacia confusa, Albizzia lebbek, Aporusa chinensis, Bombax malabaricum, Castanopsis fissa, Liquidambar formosana, Litsea glutinosa, Machilus breviflora, Pinus elliottii, andTristania conferta), belonging to eight families, were transplanted to two sites, one with a high concentration of landfill gas in the cover soil (high-gas site, HGS) and the other with a relatively low concentration of gas (low-gas site, LGS). Apart from the gaseous composition, the general soil properties were similar. A strong negative correlation between tree growth and landfill gas concentration was observed. A laboratory study using the simulated landfill gas to fumigate seedlings of the above species showed that the adventitious root growth ofAporusa chinensis, Bombax malabaricum, Machilus breviflora, andTristania confera was stimulated by the gas, with shallow root systems being induced.Acacia confusa, Albizzia lebbek, andLitsea glutinosa were gas-tolerant, while root growth ofCastanopsis fissa, Liquidambar formosana, andPinus elliottii was inhibited. In most cases, shoot growth was not affected, exceptions beingBombax malabaricum, Liquidambar formosana, andTristania conferta, where stunted growth and/or reduced foliation was observed. A very high CO₂ concentration in cover soil limits the depth of the root system. Trees with a shallow root system become very susceptible to water stress. The effects of low O₂ concentration in soil are less important than the effects of high CO₂ concentration.Acacia confusa, Albizzia lebbek, andTristania conferta are suited for growth on subtropical completed landfills mainly due to their gas tolerance and/or drought tolerance.     

Assessment of medical care costs of injuries due to alcohol-related motor vehicle crashes

The purpose of this study was to estimate the total medical care costs of individuals injured in motor vehicle crashes and in crashes where alcohol was involved. Crashes were studied that involved 2,728 vehicle occupants and 191 pedestrians with injuries as reported in 1979 by the National Accident Sampling System, a probability sample of all motor vehicle crashes occurring in the united States. Medical care costs were assigned by using Abbreviated Injury Scale codes in accordance with other published research. Determination of alcohol involvement was based on crash characteristics. Results indicate that 20.2 % of medical care costs for motor vehicle crash injuries may be due to crashes where alcohol was involved. It was estimated that alcohol-related motor vehicle crashes cost between $434 million and $483 million in medical care alone in the United States in 1979.     

Comparison of Four <Emphasis Type="Italic">Sesbania</Emphasis> Species to Remediate Pb/Zn and Cu Mine Tailings

A 6-month greenhouse pot trial was performed, aimed at screening appropriate Sesbania species for remediation of Pb/Zn and Cu mine tailings. Performances of young seedlings of four Sesbania species (S. cannabina, S. grandiflora, S. rostrata, and S. sesban) were compared with and without inoculation of rhizobia. Seedlings were planted in two types of tailings amended with garden soil or garden soil mixed with river sediment. The results indicated that inoculated plants generally produced a higher biomass than samples without inoculation. Pb/Zn mine tailings containing rather high concentrations of total and water-soluble Cu, Pb, and Zn were toxic to plant growth compared with Cu mine tailings, according to the growth performance of the four species. Sesbania sesban and S. rostrata showed superior growth performance, compared to the other two species. Thus, they can serve as pioneer species to modify the barren environment, by providing organic matter and essential nutrients such as nitrogen, upon decomposition, in a relatively short period of time. This is especially true for S. rostrata, which is an annual plant that forms both stem and root nodules. However, a longer-term field trial should be conducted to investigate if superior species can beneficially modify the habitat for the growth of subsequent plant communities.     

Response of Ceriodaphnia dubia to ionic silver: discrepancies among model predictions, measured concentrations and mortality

Silver thiosulfate, often a waste product of photoprocessing, is less bioavailable or toxic to aquatic organisms than is ionic silver. We conducted duplicate 48-h Ceriodaphnia dubia tests in reconstituted laboratory water using treatments of 92.7 nM Ag+ with various concentrations of thiosulfate. Expected Ag+ concentrations were generated for thiosulfate treatment levels using MINEQL + chemical equilibrium modeling. Ag+ concentrations in treatments were determined using a novel silicon-based sensor. Based on predicted Ag+ and published 48-h LC50 values for C. dubia, we did not expect to observe adverse effects. Yet, 100% mortality was observed at low thiosulfate treatments, whereas > 85% and > 95% survival was observed at higher thiosulfate treatment levels, respectively. Our results indicate that biotic responses match the sensor-based Ag+ concentrations. However, there is a discrepancy between these empirical results and responses expected to occur with Ag+ concentrations as predicted by MINEQL + chemical modeling. By correlating silicon sensor data with toxicity results obtained from our laboratory, our work clearly relates a specific chemical form (Ag+) to toxicity results.