Microcosms, laboratory

All these factors should be carefully considered in the design and implementation of any bioremediation program. The rather pessimistic views presented above are supported by quoting the succinct conclnsions of a study on PAH loss in laboratory microcosms using soil from a site contaminated with PAHs from a previous gas manufacturing facility (Erickson et al. 1993). 

Model parameter estimation by laboratory, microcosm, or pilot plant studies followed by field application. 

Endrin released to water will adsorb to sediments or bioaccumulate in fish and other aquatic organisms. Both bioaccumulation and biomagnification of endrin were reported to occur in an aquatic laboratory microcosm system (Metcalf et al. 1973). In terrestrial ecosystems, endrin transformation products (endrin ketone, endrin aldehyde, and endrin alcohol) have been measured in plants grown on endrin-treated soil (Beall et al. 1972 Nash and Harris 1973). 

Soil. In laboratory microcosm experiments kept under aerobic conditions, half-lives of 7.2 and 1.7 d were reported for 2-chlorophenol in an acidic clay soil (<1% organic matter) and slightly basic sandy loam soil (3.25% organic matter) (Loehr and Matthews, 1992). In a nonsterile clay loam soil, a loss of 91% was reported when 2-chlorophenol was incubated in a nonsterile clay loam at 0 °C. Nondetectable levels of 2-chlorophenol was reported in sediments obtained from a stream at 20 °C after 10 to 15 d (Baker et ah, 1980). 

Soil. In laboratory microcosm experiments kept under aerobic conditions, half-lives of 5.1 and 1.6 d were reported for 2-methylphenol in an acidic clay soil (<1% organic matter) and slightly basic sandy loam soil (3.25% organic matter) (Loehr and Matthews, 1992). 

Kassen, R. Bockiln, A. Bell, G. Rainey, P.B. (2000) Divwsity peaks at intermediate productivity in a laboratory microcosm. Nature, 406, 508-12. 

Direct measurement of putrefaction is problematic. In laboratory microcosms in which radiolabeled (35S) algae were allowed to settle and decay on top of lake sediments, a net release of less than 5% of the to the water column was observed, and all release occurred within the first 2 weeks (38). However, ongoing microbial uptake of sulfate from the water column may have obscured further release. Maximal potential rates of cystine degradation were estimated by Jones et al. (81) to range from 0.001 to 50 xmol/L per day in Blelham Tarn sediments and by Dunnette (82) to range from 28 to 47 xmol/L per day in sediments from two lakes. Similar measurements of potential rates of hydrolysis of sulfate esters (83) tremendously overestimated the rates calculated by mass balance to occur in sediments of Wintergreen Lake (73). A better understanding of putrefaction is needed to predict retention and concentrations of S in sediments. 

Laboratory microcosms with Little Rock Lake sediments inoculated with 35S042- also show a gradual increase in organically bound 35S (< 1% to > 30% of reduced S over three months) and "CRS (20% to > 50%) whether incubated anaerobically or under oxic water columns. Sediments incubated under oxic water columns showed increasing incorporation of 3SS into fulvic and humic acids after a one-month delay (up to 30% of reduced S). Whether incorporation into fulvic and humic acids followed partial oxidation to polysulfides or elemental S (cf. 46-491 is not known. However, AVS accounted for < 10% of reduced 35S in our microcosms. Recent marine studies have also shown that H S (50-521 can be directly incorporated into acrylate, a breakdown product of i-mmethylsulphoniopropionate (DMSP), but the significance of this reaction in freshwater sediments has not been examined. 

Gruessner B, Watzin MC. 1996. Response of aquatic communities from a Vermont stream to environmentally realistic atrazine exposure in laboratory microcosms. Environ Toxicol Chem 15 410-419. 

US Environmental Protection Agency [USEPA]. 2002b. Generic freshwater (laboratory) microcosm test guideline. Washington (DC) US Environmental Protection Agency. 

Portier RJ. 1985. Comparison of environmental effect and biotransformation of toxicants on laboratory microcosm and field microbial communities. In ASTM Spec Tech Publ Validation and Predictability of Laboratory Methods for Assessing the Fate Effects of Contaminants in Aquatic Ecosystems, Philadelphia, PA, 865 14-30. 

There is a wide spectrum of these microcosm and mesocosm higher-tier test systems available, from laboratory microcosms to outdoor mesocosms, enclosures, and artificial streams (ECETOC 1997). Fish are usually not included, and this is a problem if single-species tests suggest that fish are more sensitive than algae or invertebrates (Girling et al. 2000). 

Anaerobic reductive dechlorination of chiral PCBs confirmed that microbial reductive dechlorination in situ was possible in Lake Hartwell [163]. Microcosms with sediments from the same cores [156] spiked with racemic PCB 132 reductively meto-dechlorinated this congener nonenantioselectively to PCB 91, which in mrn was stereoselectively meta-dechlorinated to achiral PCB 51 (Figure4.12). Similarly, PCB 149wasnonstereoselectively /jflra-dechlorinated to PCB 95, in turn enantioselectively meta-dechlorinated to achiral PCB 53 [163]. The enantiomer preferences for PCB 149 dechlorination were consistent between the laboratory microcosms [163] and field observations, suggesting possible similarities in the microbial consortia in both cases. However, PCB 132 was nonracemic in the cores [156], suggesting that either the microbial consortia and/or environmental conditions affecting microbial activity were different between the laboratory and in situ. Much remains unknown about the microbial strains and enzymes involved in PCB anaerobic reductive dechlorination or the factors controlling stereospecificity. 

Figure 4.12 Reductive dechlorination of PCB 132 enantiomers and products in laboratory microcosms of Lake Hartwell sediments over time concentrations (A-C), enantiomer fractions for PCBs 132 (D) and 91 (E). Autoclaved control with racemic PCB 132 added (open circles, crosshatched bars), live treatments with racemic 132 added (filled circles, filled bars). Racemic value of EF —0.5 denoted by dashed line. (Reproduced with permission from Environmental Science and Technology, Changes in Enantiomeric Fractions during Microbial Reductive Dechlorination of PCB 32, PCB 149, and Arocior 1254 In Lake Hartwell Sediment Microcosms, by Usarat Pakdeesusuk, W. jack Jones et al., 37(6), 1100-1107. Copyright (2003) American Chemical Society)...

In laboratory microcosms, ira 5-permethrin was selectively degraded compared to the other diastereomer, cw-permethrin, by six bacterial strains [19]. These strains also preferentially biotransformed 15-cw-bifenthrin over their antipodal l/ -cw-enantiomers, which were more toxic to daphnids [19]. Enantioselectivity was more pronounced for cw-permethrin than for cw-bifenthrin, and was strain-dependent. The (—)-enantiomer of both pyrethroids was preferentially depleted in sediments adjacent to a plant nursery, suggesting that in situ microbial biotransformation was enantioselective [20]. Although all enantiomers of permethrin were hydrolyzed quickly in C-labeled experiments in soils and sediments, the degradates of both cis- and irara-permethrin s -enantiomers were mineralized more quickly than those of the 5-enantiomer, while degradation products of cA-permethrin were more persistent than those of the trans-isomex [185]. Enantioslective degradation of fenvalerate in soil slurries has also been reported [83]. These smdies underscore how enantiomer-specific biotransformation can affect pyrethroid environmental residues, the toxicity of which is also enantiomer-dependent [18-20]. 

Taylor B. R. and Parkinson D. (1988a) Aspen and pine leaf litter decomposition in laboratory microcosms 2. Interactions of temperature and moisture level. Can. J. Botany Rev. Can. Botanique 66(10), 1966-1973. 

Because of the deficiencies of single-species toxicity tests, alternative approaches are being evolved to address the structural and functional processes of an ecosystem. Multispecies tests include the use of laboratory microcosms, outdoor ponds, experimental streams, and enclosures. There are no standardized procedures for these tests. They are conducted with plant and animal species obtained from laboratory cultures and biota collected from natural sources. They can be conducted indoors or outdoors. The toxic effects, in addition to those used for single-species tests, are determined for structural parameters, such as community similarity, diversity, and density, and for functional parameters, such as community respiration and photosynthesis. Effects on these parameters are reported as the NOEC and LOEC. 

Terrestrial microcosms also see a comparable range in size and complexity. A microbial community living within the soil in a test tube can be used to examine biodegradation. A soil core is comparable in size and utility to the laboratory microcosms described above. In some cases terrestrial microcosms can be established with a variety of plant cover and include small mammals and insects. Field plots are the terrestrial equivalent of the larger outdoor... 

Sugiura, K. 1992. A multispecies laboratory microcosm for screening ecotoxicolog-ical impacts of chemicals. Environ. Toxicol. Chem. 11 1217-1226. 

Until more data can be obtained, the cause-effect of the second oscillation cannot be determined. However, the use of multivariate analysis detected an unexpected result, one providing a new insight into the dynamics of even the relatively simple laboratory microcosm. 

Kelly, J.J., Haggblom, M. and Tate, R.L. (1999) Changes in soil microbial communities over time resulting from one time application of zinc a laboratory microcosm study. Soil Biology Biochemistry, 31, 1455-1465. 

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