Enumeration and factors influencing the relative abundance of a denitrifier, Pseudomonas sp. JR12, entrapped in alginate beads

The relative abundance of the denitrifier, Pseudomonas sp. JR12, was examined in an alginate-based entrapment complex under non-sterile, denitrifying conditions. Immuno-labeling of the Pseudomonas inoculant followed by flow cytometry (FCM) was used for determination of the relative abundance of this bacterium under the various incubation conditions. Additional information on the relative abundance of the inoculant was obtained by a quantitative enzyme-linked immunosorbent assay (ELISA) and results obtained by FCM and ELISA were compared. Ambient nitrate levels controlled the successful, long-term proliferation of the inoculant. At low ambient nitrate levels, Pseudomonas sp. remained the dominant microorganism during incubation. Higher ambient nitrate concentrations, attained by either decreasing the inoculum size of Pseudomonas sp. or raising inlet nitrate concentrations of the medium supplied to the incubation vessels, resulted in a gradual shift toward other, nitrite-accumulating denitrifiers. Thus far, most studies on the use of entrapped microorganisms for bioremediation purposes have been conducted under controlled laboratory conditions. Based on this study, conducted under non-sterile laboratory conditions, it is concluded that in-situ bioremediation using entrapped target microorganisms is bound to fail without a proper understanding of the factors that cause the target microorganism to out-compete undesired microbial invaders. Furthermore, based on the close agreement between the two detection methods used, it is concluded that flow cytometry provides a rapid and accurate tool for the detection of the relative abundance of immuno-labeled target organisms in heterogeneous microbial populations.     

Tropical agricultural residues and their potential uses in fish feeds: the Costa Rican situation

In Costa Rica as many other tropical countries, the disposal problem of agricultural wastes is widely recognized but efforts to find solutions are not equal for different sectors. This study describes the situation of major agricultural residues in Costa Rica, identifying the activities with higher amounts produced and, the potential use of these residues in fish feeds. In Costa Rica, during the 1993-1994 production season, major agricultural sectors (crop and livestock) generated a total amount of 3.15-3.25 million MT of residues (classified in by-products: used residues and wastes: not used residues). Some residues are treated to turn them into valuable items or to diminish their polluting effects (e.g., the so-called by-products). About 1.56-1.63 million MT of by-products were used for different purposes (e.g. fertilization, animal feeding, fuel, substrates in greenhouses). However, the remainder (1.59-1.62 million MT) was discharged into environment causing pollution. About 1.07-1.2 million MT wastes came from major crop systems (banana, coffee, sugarcane and oil palm) whereas the remainder came from animal production systems (porcine and poultry production, slaughtering). These data are further compared to residues estimates for the 2001-2002 production season coming from the biggest crops activities. Unfortunately, most of the studied wastes contain high levels of moisture and low levels of protein, and also contain variable amounts of antinutritional factors (e.g., polyphenols, tannins, caffeine), high fibre levels and some toxic substances and pesticides. All these reasons may limit the use of these agricultural wastes for animal feeding, especially in fish feeds. The potential use of the major vegetable and animal residues in fish feeds is discussed based on their nutritional composition, on their amount available over the year and on their pollution risks. Other constraints to use these wastes in fish feeds are the extra costs of drying and, in most cases, of transportation from several dispersed locations. It was stated that most interesting wastes are rejected green banana and coffee pulp.     

Automated and continuous redox potential measurements in soil

Redox potential (Eh) describes the electrical state of a matrix. In soils, Eh is an important parameter controlling the persistence of many organic and inorganic compounds. A popular, but also criticized, manual measuring method makes use of a small tip of Pt placed on a copper wire that is placed in the soil; a reference electrode is placed in the same soil at a fixed distance. Fluctuations in redox potential values measured in the soil can be very large and depth-dependent. This will be overlooked when making single-point measurements. We developed the datalogger Hypnos 2.0 for continuous redox potential and temperature measurements at various depths in the soil and without disturbance of the site. Hypnos is field-deployable, relatively cheap, and runs on batteries. The datalogger can use a "sleep mode" between sampling events. In sleep mode, there is no constant voltage on the Pt wire or the reference electrode, but there is only a short pulse during sampling. We did not measure an effect of this short pulse on the measured redox potential. In sandy soils in mesocosms and in a salt marsh soil we measured changes in the Eh as large as from -400 to +100 mV within 4 d, and daily cycles of 200 mV. Both absolute redox potential values and their diurnal variations were depth-dependent. Because single redox measurements are insufficient in describing redox conditions in some soil systems, Hypnos can be a powerful tool when studying the effects of fluctuating redox conditions on metal availability and pollutant degradation.     

The contemporary Oceania zinc cycle: one-year stocks and flows

The material flow approach provides a framework from which to address resource management and estimate gross environmental impacts, both spatially and temporally. In this article, the major flows of zinc in Oceania over its entire life-cycle are examined; these include production (mining, milling, and refining), fabrication and manufacturing of semi- and finished products, use, and the waste management system. Comprehensive mass balances were applied to determine the zinc flows, including the quantities of zinc entering stocks in waste and in-use reservoirs. The Oceania cycle shows that substantial amounts of zinc (about 1120Gg/year) are mined on the continent. The total flow of zinc in finished products entering the use stage is about 8.6kg/(capita.year), substantially exceeding the zinc flow in discarded products. This difference, about 7.2kgZn/(capita.year) on average, is added to the in-use reservoir, largely for galvanizing applications in domestic construction and transportation. Less than 60% of all discarded zinc entering the waste management system is recycled. Much of the remaining discarded zinc is diluted into other waste streams, where recovery and recycling are probably not economically feasible.     

Spiking of performance reference compounds in low density polyethylene and silicone passive water samplers

A method for spiking performance reference compounds (PRCs) into low density polyethylene (LDPE) and silicone polymers is described. This method is based on equilibration of the polymers in aqueous/methanolic solutions of PRCs. Equilibration times range from minutes to hours for perdeuterated polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) with a hydrophobicity in the range 3.9 < logKow < 7.7. Best results were obtained for methanol-water ratios of 80/20 (v/v). The method allows for the use of PRCs for in situ calibration of the uptake kinetics of these solvent-free sampling phases in a similar way as for semipermeable membrane devices (SPMDs).     

Characterization of the leaching behaviour of concrete mortars and of cement-stabilized wastes with different waste loading for long term environmental assessment

The leaching behaviour of cement-based products-both construction products and cement-stabilized wastes--have been shown to be similar after assessing the leaching characteristics by means of a pH dependence leaching test. This procedure is particularly suited to identifying the chemical speciation of materials. Geochemical modelling has shown a number of solubility controlling phases in this largely inorganic matrix, that can very well explain the observed leaching patterns as a function of pH. Understanding these relationships allows the prediction of leaching behaviour under other exposure conditions and to improve the ultimate quality of products, if so desired. The role of ettringite-type phases for the binding of oxyanions in the pH range above pH 12 has been identified before and confirmed in this work. The order of incorporation follows from the ratio between the maximum leachability at mildly alkaline pH and at high pH. Increased levels of sulfate negatively influence the binding of oxyanions in cement-stabilized waste through site competition.     

Dissolution kinetics of heavy metals in Dutch carbonate- and sulfide-rich freshwater sediments

In two sulfide-rich freshwater sediments from the Biesbosch and Kromme Rijn River in the Netherlands differing in carbonate content and acid volatile sulfide (AVS) content, metal and sulfide dissolution kinetics were studied at different acid concentrations by varying both the procedure of acid addition and the extraction time. The establishment of equilibrium was monitored by measuring the pH in time, which reached a near constant value. The equilibrium pH was reached quickly when large amounts of acid were added and slowly when small amounts of acid were added. This observation was confirmed by the yield of extracted metals after either a 45-min or 24-h extraction over a pH range from 0 to 5. The pH factor seemed to be of more influence than time for the dissolution of metals. The amount of extracted metals was highly dependent on the metal itself due to its physico-chemical behavior. Although the sediments studied varied in carbonate content, acid volatile sulfide (AVS), and total metal content, the extracted fraction of metals compared with their total content in the sediment was similar for most metals. Finally, the AVS content as well as the ratio of simultaneously extracted metals (SEM; sum of Cd, Cu, Ni, Pb, and Zn) to AVS decreased with increasing pH. Because the SEM to AVS ratio may be used to set environmental quality criteria for the sediment compartment, this observation is of significance.     

Effects of soil variability and weather conditions on pesticide leaching--a farm-level evaluation

In line with European regulations, Dutch law imposes an environmental threshold of 0.1 microg L(-1) on pesticide concentrations in ground water. During registration, the risk of exceeding this threshold is assessed through simulations for one or a few standard scenarios that do not reflect spatial variability under field conditions. The introduction of precision agriculture, where soil variability is actively managed, can increase control over pesticide leaching. This study presents a step-wise evaluation of the effects of soil variability and weather conditions on pesticide leaching. The evaluation was conducted on a 100-ha arable farm and aimed at identifying opportunities for precision management. As a first step, a relative risk assessment identified pesticides presenting a relatively high risk to the environment. Second, the effect of weather conditions was analyzed through 20 years of simulations for three distinct soil profiles. Results were summarized in cumulative probability plots to provide a probabilistic characterization of historical weather data. The year matching 90% probability (1981) served as a reference to simulate pesticide leaching from 612 soil profiles. After interpolation, areas where concentrations exceeded the environmental threshold were identified. Out of a total of 19 pesticides, isoproturon [N-dimethyl-N'-(4-(1-methylethyl)phenyl)urea], metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], and bentazon [2,1,3-benzothiadiazin-4(3H)-one, 3-isopropyl-, 2,2-dioxide] showed the highest risk for leaching. Leaching was strongly affected by soil variability at the within-field, field, and farm levels. Opportunities for precision management were apparent, but depended on the scale level at which environmental thresholds were implemented. When legislation is formulated in this issue, the presented step-wise evaluation can serve as a basis for identification and precision management of high-risk pesticides.