Bioassay Species

Both lantana and common purslane are weed pests in some crops. Common purslane root exudates inhibited soybean growth but showed stimulation in other bioassays reported in this paper. This may be a concentration and bioassay species dependent effect, since the effect of any toxin varies according to concentration and bloassay species (12). Lantana root exudates showed the strongest inhibitory effect on soybean growth of any of the species tested. Lantana is not found in soybean fields but is a weed pest in some areas in citrus orchards. Holm (13) included lantana, johnsongrass, and cogongrass in his list of the worst weed pests in the world. 

Abdul-Wahab and Rice (9) found that boiling water extracts of johnsongrass leaves inhibited germination and seedling growth of several bioassay species at concentrations 80 times that used in this present study. 

A useful resource related to carcinogenicity, includes a wide array of publications from the Carcinogenic Potency Project. The references include papers on methodological analysis of the relevance of carcinogenicity prediction from bioassays, species comparisons, target organs, mechanism of carcinogenesis, risk assessment techniques, possible cancer hazards of natural and synthetic chemicals, and causes and prevention of cancer. 

How representative a model system is can be determined to some extent by testing other bioassay species and soils in the model system chosen and by comparing the biological and physicochemical characteristics and processes of model and field systems. The following considerations are thus worth noting ... 

I would suggest that given the right condihons and bioassay species this approach may also turn out to be useful not only for phenolic acids but also for other suspected allelopathic agents. The benefit of this approach is that the relationships between seedling inhibihon and stimulation of phenolic... 

Literally hundreds of plant extracts have been tested for bioactivity and shown to be active. In fewer cases, compounds have been isolated from these extracts and tested, and individually they often have shown activity. Scores of commercially available natural products also have been tested in a myriad of bioassays. Paper after paper has been written purporting that many of them are allelopathic. Such studies are done quickly and, unfortunately, often carelessly. The common flaw of most of these laboratory reports is that they fail to consider such obvious essentials as the need to test for activity of chemicals at concentrations in which they occur in nature use appropriate bioassay species that occur in the field, rather than the traditional, easily obtained crop species such as lettuce or tomato and test mixtures of compounds that simulate nature s release of chemicals into the soil, and in which synergistic effects are often commonplace. Thus, because of such neglect, there is both garbage and confusion in the literature. Many reported effects are not real, and probably many real ones have been overlooked simply because the bioassay used was faulty. 

Maximum acceptable concentiation figures expressed as fractions of 96 h for most sensitive species in given area. The 96 h is that concentration of a substance which kills 50% of the test species within 96 h under standard bioassay conditions. 

It is not appropriate to generali2e the carcinogenicity of this class of compounds. Nitrofura2one appears to increase the incidence of benign mammary tumors in rats. The tumorigenic activity of fura2ohdone is expressed by an increase in the incidence of spontaneous tumors in both mice and rats. Bioassays of nitrofurantoin in several species of mice and rats failed to reveal any evidence of direct tumorigenic activity. Ovarian tumors have been reported in B C F mice, but these are beheved due to an indirect expression of toxicity (14,15). 

Bioassays procedures have been developed in species such as chicks which have been fed a niacin-deficient diet. Due to the fact that, for example, tryptophan is a biological precursor of niacin, niacin can be produced from other sources (55). As a result, the tryptophan content of the diet has to be monitored carefully for accurate results. 

Animal and Human Toxicity. The acute toxicity of lindane depends on the age, sex, and animal species, and on the route of adrninistration. The oral LD q in mice, rats, and guinea pigs is 86, 125—230, and 100—127 mg/kg, respectively. In contrast, most of the other isomers were considerably more toxic (94,95). Some of the other toxic responses caused by lindane in laboratory animals include hepato- and nephotoxicity, reproductive and embryotoxicity, mutagenicity in some short-term in vitro bioassays, and carcinogenicity (80). The mechanism of the lindane-induced response is not known. Only minimal data are available on the mammalian toxicides of hexachlorocyclopentadiene. 

Several recent expert reviews and workshops have discussed the effects of endocrine disruption on wildlife and especially invertebrate species. These include the EU workshop on the impact of endocrine disrupters on human health and wildlife (Weybridge, 1996), the lEH workshop (Leicester, May 1997), the Environment Agency Consultative report (January 1998) and the Tyndall Forum at the Royal Institution (February 1998). They have concluded that endocrine disruption may have far-reaching adverse consequences for biodiversity and the sustainability of natural ecosystems. More comprehensive bioassay systems are required to identify and assess chemicals alleged to produce endocrine modulating effects. 

The mysid shrimp, Mysidopsis bahia, is the test organism for the liquid and suspended particulate phases. This species has been shown to be exceptionally sensitive to toxic substances and is considered to be a representative marine organism for bioassay testing by EPA. An LCj, is determined the suspended particulate phase (SPP) bioassay tests. 

Increased mortality was observed in both male rats (at doses of 20.4 mg/kg/day and above) and male mice (at doses of 0.46 mg/kg/day and above) in a 2-year bioassay conducted by the National Cancer Institute (NCI 1978). The authors attributed the excessive mortality in the male rats to treatment-related toxic nephropathy. The high mortality in male mice was possibly due to fighting since no other treatment-related cause for the deaths could be determined. Survival in females of both species was unaffected by endosulfan (NCI 1978). However, survival was significantly decreased in female rats that consumed 5 mg/kg/day for 2 years (FMC 1959b), and in female mice that consumed approximately 2.9 mg technical endosulfan/kg/day for 2 years (Hack et al. 1995 Hoechst 1988b). In these studies, survival in male rats was not affected at 5 mg/kg/day for 2 years (FMC 1959b) and survival in male mice was not affected at 2.51 mg/kg/day for 2 years (Hoechst 1988b). 

Garrison, P.M., Tullis, K., and Aarts J.M.M.J.G. et al. (1996). Species specific recombinant cell lines as bioassay systems for the detection of dioxin-like chemicals. Fundamental and Applied Toxicology 30, 194-203. 

Field and laboratory bioassay of chemosignals from related sympatric and allopatric species (overlapping and discrete distributions) are essential to an understanding of the relatedness or otherwise of functionally active compounds. The semiochemicals involved in speciation surely utilise the main and vomeronasal senses, but their relative contributions cannot be predicted at present. 

In our efforts to detect and isolate the allelcpathic agents from tall fescue and several other grass species, we extracted the detached plant material with water and/or organic solvents. Either solvent extraction method yielded extracts that were inhibitory to the seed germination and seedling growth in our bioassay systems. 

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