Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are toxic metals, toxic chemicals, microbe neurotoxins, radiation particles and even specific neurotransmitters when the system is out of balance. Also some types of venom, e.g. from the puff adder (Bitis arietans) or brown recluse spider (Loxosceles reclusa) are toxic to cells. Source: Wikipedia (en)