Procedures are described for testing freshwater organisms in the laboratory to evaluate the toxicity or bioaccumulation of contaminants associated with whole sediments. Sediments may be collected from the field or spiked with compounds in the laboratory. Toxicity methods are outlined for two organisms, the amphipod Hyalella azteca and the midge Chironomus tentans. The toxicity tests are conducted for 10d in 300-mL chambers containing 100 mL of sediment and 175 mL of overlying water. Overlying water is renewed daily and test organisms are fed during the toxicity tests. The endpoint in the toxicity test with H. azteca is survival and the endpoints in the toxicity test with C. tentans are survival and growth. Procedures are primarily described for testing freshwater sediments; however, estuarine sediments (up to 15% salinity) can also be tested with H. azteca. Guidance for conducting 28-d bioaccumulation tests with the oligochaete Lumbriculus variegatus is provided in this manual. Overlying water is renewed daily and test organisms are not fed during bioaccumulation tests. Methods are also described for determining bioaccumulation kinetics of different classes of compounds during 28-d exposures with L. variegatus.

Methods for measuring the toxicity and bioaccumulation of sediment-associated contaminants with freshwater invertebrates

▪ Abstract The vast surface of the plant axis, stretching from root tips occasionally buried deeply in anoxic sediment, to apical meristems held far aloft, provides an extraordinarily diverse habitat for microorganisms. Each zone has to a greater or lesser extent its own cohort of microorganisms, in aggregate comprising representatives from all three primary domains of life—Bacteria, Archaea, and Eucarya. While the plant sets the stage for its microbial inhabitants, they, in turn, have established varied relationships with their large partner. These associations range from relatively inconsequential (transient epiphytic saprophytes) to substantial (epiphytic commensals, mutualistic symbionts, endophytes, or pathogens). Through recent technological breakthroughs, a much better perspective is beginning to emerge on the nature of these relationships, but still relatively little is known about the role of epiphytic microbial associations in the life of the plant.

The Ecology and Biogeography of Microorganisms on Plant Surfaces.

Major metal-binding phases in the aerobic layer of sediments are iron and manganese oxyhydroxides (FeOOH and MnOOH) and particulate organic carbon (POC). The acid-volatile sulfide (AVS) model propo...

Ecotoxicology of metals in aquatic sediments: binding and release, bioavailability, risk assessment, and remediation

Horizontal gene transfer (HGT) plays an important role in the evolution of life on the Earth. This view is supported by numerous occasions of HGT that are recorded in the genomes of all three domains of living organisms. HGT-mediated rapid evolution is especially noticeable among the Bacteria, which demonstrate formidable adaptability in the face of recent environmental changes imposed by human activities, such as the use of antibiotics, industrial contamination, and intensive agriculture. At the heart of the HGT-driven bacterial evolution and adaptation are highly sophisticated natural genetic engineering tools in the form of a variety of mobile genetic elements (MGEs). The main aim of this review is to give a brief account of the occurrence and diversity of MGEs in natural ecosystems and of the environmental factors that may affect MGE-mediated HGT.

Horizontal Gene Exchange in Environmental Microbiota

Quantitative in situ determination of conjugative gene transfer in defined bacterial biofilms using automated confocal laser scanning microscopy followed by three-dimensional analysis of cellular biovolumes revealed conjugation rates 1,000-fold higher than those determined by classical plating techniques. Conjugation events were not affected by nutrient concentration alone but were influenced by time and biofilm structure.

High Rates of Conjugation in Bacterial Biofilms as Determined by Quantitative In Situ Analysis

Dredging impact on an urbanized Florida bayou: effects on benthos and algal-periphyton.

Effect of root exudates and bacterial metabolic activity on conjugal gene transfer in the rhizosphere of a marsh plant

Seeds of eleven woody species were exposed to 2.3 cm/wk of simulated sulfuric acid rain at pH values of 3.0, 3.5, or 4.0, or to a simulated control rain at approximately pH 5.6. All treatments also contained a neutral mixture of cations and anions based on concentrations reported for Hubbard Brook, N.H. Seeds or seedlings were subject to ambient conditions, except deposition. Seeds were planted in winter, 1977; seedlings were harvested the following summer. The dry weights of the top and roots of each seedling were recorded. Although eight species were affected by simulated acid rain, the direction and magnitude of effects varied with species and with treatment. Seedling emergence was stimulated by at least one acid treatment for four species, while root growth was inhibited for one species. Except for one species, whose emergence rate and top growth were both affected, effects were confined to one measured parameter.

The Effect of Simulated Acid Rain on Seedling Emergence and Growth of Eleven Woody Species

Effects of Sulfuric Acid Rain on Major Cation and Sulfate Concentrations of Water Percolating Through Two Model Hardwood Forests 1

Methods are described for toxicity testing of water and sediment with two varieties of the freshwater marsh plant Echinochloa crusgalli (Linneaus) Palisot de Beauvois (Poaceae), and complex effluents. Two tests are described: a seed germination and early seedling growth test in water, and a survival and seedling growth test in natural and synthetic sediments. Effects of effluents from a sewage treatment plant, tannery, textile mill, pulp and paper mill, coking plant and sewage treatment plant included inhibition of germination, chlorophyll synthesis and growth. The tests with rooted marsh plants were sensitive to pollutants and detected toxicity of a range of pollutants in water and sediment. Synthetic sediments similar to natural sediments allowed toxicity tests to be done under carefully controlled conditions of particle size distribution, organic content, pH, electrode potential (Eh) and cation exchange capacity (CEC).

David E. Weber

Papers

Dredging impact on an urbanized Florida bayou: effects on benthos and algal-periphyton.

Effect of root exudates and bacterial metabolic activity on conjugal gene transfer in the rhizosphere of a marsh plant

The Effect of Simulated Acid Rain on Seedling Emergence and Growth of Eleven Woody Species

Effects of Sulfuric Acid Rain on Major Cation and Sulfate Concentrations of Water Percolating Through Two Model Hardwood Forests 1

Toxicity tests of effluents with marsh plants in water and sediment