Toxicity Test

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INTRODUCTION:
Toxicity test evaluates the deleterious effects of chemicals on humans, animals, plants, environment following single (acute) or repeated (long term) exposure (Arwa and Vladimir, 2016). Safety evaluation of chemicals is very important for their development and approval for human uses (Gallagher, 2003; Peers et al., 2012).
In risks assessment, there is no doubt that the best test species for humans are humans since accurate extrapolation of animal data directly to humans cannot be guaranteed due to interspecies variation in anatomy, physiology and biochemistry (Gallagher, 2003). However, due to human ethical reasons, such substances are required to be tested using animal models before they are subjected to clinical trials in humans
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The LD50 (50 % lethal dose) test) was introduced in 1920 by J. W. Trevan to determine the lethal dose of individual chemicals. It is usually the first test conducted for every chemical before further toxicity tests are carried out. It is used for estimating the potential hazards of chemicals to humans and its major endpoint is death however, non-lethal acute effect may occur as signs of toxicity depending on the chemical being tested. Animal species used include; rats, mice, rabbits, and rabbits (Maheshwari and Shaikh, …show more content…
In the first phase, nine (9) animals are divided into three (3) groups of three (3) animals each and then administered 10, 100 and 1000 mg/kg body weight of the test substance in other to establish the dose range producing any toxic effect. The number of death in each group is recorded after 24-hours. In the second phase, four doses of the test substance selected based on the results of phase 1 are administered to four groups of one animal each. After twenty four hours, the number of death is recorded and the LD50 is calculated as the geometric mean of the highest non-lethal dose (a) and the least toxic dose (b). LD50 = √(a ×b) (Lorke, 1983; Enegide et al, 2013).
Miller and Tainter method, 1944:
Miller and Tainter method established in 1944 involves the use of fifty (50) animals which are divided into five (5) groups of ten (10) animals each. Signs of toxicity and death are observed and recorded on animals after administration and the LD50 is calculated using probit analyses table. Probit values are plotted against the log dose and the dose corresponding to probit five (5) becomes the LD50 value (Randhawaet al., 2009; Saganuwa,

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