Many of the substances that humans consume on a regular basis as parts of their basic diet actually contain harmful toxins. Rice, barbecued meat and drinking water all pose threats to human health as hosts to potent toxins, carcinogens and opportunistic pathogens. In many cases, the rise in concentrations of these harmful substances is a direct result of human activity, such as the use of harmful pesticides in crops and even advances in green technology. Risk assessment can be a useful tool for determining the actual threat to human health with numerous variables between population groups and degrees of uncertainty.