Bioassays soil testing

These are tests that are established within the academic community as monitors of chemical exposure and chemical effect. Unlike the procedures discussed in section 6.2, standards do not exist for these tests. Development instead can be tracked via a series of scientific papers. Some methods are long established in soil ecology and ecotoxicology. Examples include invertebrate bioassays, soil enzyme assays and litterbags. In contrast, a number of methods, such as bait lamina and some biochemical assays (e.g. lysosomal membrane stability), have been developed more recently but have passed quickly into widespread use. 

Figure 10.4 represents a summary of bioassays distinguishing between whole soil and elutriate tests reflecting different assessment objectives. Whilst whole soil tests may preferably be used for ecological assessments (e.g. the investigation of habitat functions of soil), testing of elutriates provides information on the mobility of contaminants and the retention capability of soil. 

Various bioassay methods have been used to detect the "natural" release of allelopathic agents. Sane authors preferred, after partial purification, to assay the extracts by petri dish methods for gemination, growth of roots or shoots and other symptoms of seedlings. The bioassays also included tests in soil or sand and also in nutrient solution (Table 3). 

Two bioassays are employed to evaluate the effect of samples on terrestrial life forms. For gas samples, the plant stress ethylene test is presently recommended. This test is based on the well-known plant response to environmental stress release of elevated levels of ethylene (under normal conditions plants produce low levels of ethylene). The test is designed to expose plants to various levels of gaseous effluents under controlled conditions. The ethylene released during a set time period is then measured by gas chromatography to determine toxicity of the effluent. For liquid and solid samples, a soil microcosm test is employed. The sample is introduced on the surface of a 5 cm diameter by 5 cm deep plug of soil obtained from a representative ecosystem. Evolution of carbon dioxide, transport of calcium, and dissolved oxygen content of the leachate are the primary quantifying parameters. 

The aqueous extracts of roots and leaves, the leachates of aerial parts, aqueous extracts of soils and in some cases organics extracts of leaves, the essential oils, and Isolated pure compounds were tested for their effects upon germination and growth of several test species from the same area. Likewise, bioassays of simultaneous germination were carried out with some of the available seeds. 

Shuman LM, Wilson DO, Ramseur EL. 1991. Testing aluminum-chelate equilibria models using sorghum root growth as a bioassay for aluminum. Water Air Soil Pollut 57-58 149-158. 

The Heavy Metal Binding Capacity (HMBC) test is a bioassay that helps to quickly determine metal bioavailability in aquatic environments. HMBC can also be applied to soils and to root exudates from aquatic and terrestrial plants. The HMBC test is based on MetPLATE, a bacterial toxicity test that selectively detects metal toxicity. 

Low molecular weight phenolic compounds have been identified in fresh leaves and in soils in which leaves of five varieties of Capsicum annuum were decomposing. Six phenolic compounds were tested in laboratory bioassays for their allelopathic... 

Bioassays using induction of the enzymes ethoxyresorufin o-deethylase (EROD) and/or arylhydrocarbon hydroxylase (AHH) in rat hepatoma H-4-IIE cells (Zacharewski et al. 1989) and modified mouse liver cells (Schuman and Hunter 1988) have been developed and tested on water, soil, and fish samples. The... 

Field and laboratory studies were conducted to determine the levels of Cd, Pb, and HCBD in various samples collected from a swamp environment in Louisiana and to assess the toxicities of As, Cd, and Hg to two species of aquatic organisms (bluegills and crawfish) indigenous to this swamp [18]. Cadmium and Pb were present in almost all collected samples. Their concentrations in fish were below the action levels set by EPA for the protection of human health. However, hazardous levels of these two elements were found in samples of crawfish, vegetation, soil, sediment, and water to some extent. Low levels of HCBD were recorded in water and sediment samples. In bioassay studies, Hg was found to be the most toxic metal, while As was the least toxic. Between the two test organisms, blue-gills appeared to be more sensitive than crawfish. Mixtures of Cd with As or Hg resulted in a combined toxic effect which was simply additive. However, a synergistic effect was recorded with the mixtures of As and Hg. 

A final means of assessing combined exposure is through the direct application of biological testing for effects-based assessment of complexly polluted media (e.g., effluents, soils, sediments). For the use of bioassays for direct assessment of complex mixtures, the reader is referred to Chapter 4. 

It should be emphasized that a complex of substances is generally involved when allelopathic interferences occur, often with each below a threshold level for impact. This is illustrated by the combinations of phenolic acids found in decomposing crop residues (25-27) and from soils (28-34). In allelopathic situations which implicate phenolic acids, soil quantities of ferulic, p-coumaric, and caffeic acids have ranged from below 10 to above 1,000 ppm for each compound (11,35). The lower end of this spectrum is below a concentration required for an effect in current bioassays. However, additive and synergistic effects have been documented for combinations of cinnamic acids (35), benzoic acids (36), benzoic and cinnamic acids (37), and p-hydroxybenzaldehyde with coumarin (38). Each of the allelochemicals in these tests was not equally toxic, but they contributed incrementally to inhibition of germination and growth. Whereas combinations of many allelochemicals have not been determined, it appears that both additive and synergistic interactions are extremely important under field conditions. 

The biological oxidation rate of sulfur foam depends on available surface area, temperature) and access of necessary nutrients, as well as on foam composition. Preliminary test data indicate that in all cases the oxidation rate is less than that of elemental sulfur. Soil pH around the foams at Dempster Highway measured two years after installation was never lower than the pH of the surrounding native soil (Figure 3). Sulfur foam s low toxicity is indicated by the LD60 of > 5 gAg (rat) and the 100% survival rate in a fish bioassay with stickleback (96 hr) (8). 

Greenhouse Bioassay. Sandy loam soil was treated with clomazone at rates ranging from 0.063 to 1.0 kg/ha and thoroughly mixed to incorporate the chemical into the soil. The bioassay was conducted by planting wheat (Triticum aestivum) and velvetleaf (Abutilon theophrasti) into the test soils and visually assessing plant injury in the form of bleaching (0 to 100 scale) 2 weeks after planting. 

The results have shown that we have developed a sensitive and specific ELISA assay for the analysis of clomazone residues from soil samples. The procedures have demonstrated good recovery of clomazone from soil, and excellent correlation of the ELISA test results with standard GLC methodology. In addition, the results of the ELISA tests demonstrate good correlation between the observed soil levels of clomazone, and crop injury when the bioassay is performed under controlled, greenhouse conditions. This assay could, therefore, be used as a more rapid and convenient analytical method over the standard GLC technique after further validation. 

Examination of these data clearly shows that none of the three compounds Is as effective as terbufos In the jar test. Perhaps the most Interesting aspect of this data Is the relative soil efficacy of the second compound compared to the first. The substitution of a methyl group for a hydrogen between the two sulfur atoms greatly enhances the soil activity of this molecule. Quantitation of the relative soil stability of these three molecules as measured by the bioassay data are collected in Table 5 using a pseudo first order kinetic analysis of the data. 

It is vital that environmental samples (such as effluents, leachates, receiving waters, sediments and soils) taken for testing with bioassays are considered representative and that the procedures adopted for the collection, storage and preparation of samples ensure that the toxicity of the sample obtained at source does not change markedly before a test is conducted. It is also vital that supporting documentation, in the form of a chain of custody record, accompanies the sample. 

Toxicity tests use biological systems to detect the presence of toxic chemicals in the samples being investigated (e.g. water, effluents, sediments, soil). The term bioassay also is used to describe a toxicity test. The idea is that the response of an organism will be representative of organisms living in the environment where the... 

---