This is one of the major factors considered in formulating State, Territory and national Guidelines. Provided that Biosolids are used in accordance with the Guidelines there is no greater risk associated with biosolids application than with other commercial fertilisers.
The USA has conducted more than 30 years of scientific research including a US Environmental Protection Authority risk assessment of biosolids use. These studies included the independent evaluation of how biosolids could directly or indirectly affect human health and the environment and established minimum safe concentrations for biosolids applications to land. It concluded that if correctly managed biosolids application to land has no adverse environmental or health impacts.
Similar research has been conducted throughout Australia in the past 15 years.
A summary of the specific Guidelines for biosolids management in Australia and New Zealand can be found here.