There are three major environmental factors that affect mutation rates, viz, temperature, certain radiations and chemicals.
Temperature as mutagens- the rate of all chemical reactions are influenced by temperature. It is not surprising that temperature can be mutagenic. It is reported that the rate of mutation is increased due to increase in temperature.
Radiations: the radiations which are important in mutagenesis are of two categories: one type is ionizing radiations such as X-rays and gamma rays;alpha and beta rays. The second type is non-ionizing radiations such as ultraviolet and visible light.
Chemical mutagens: many chemical substances have been responsible to increase the mutability of genes.