Most of the concerns about biosolids are with class B
materials. Potential concerns include the presence of
pathogenic organisms such as bacteria, protozoa and
viruses, excess salts, the presence of heavy metals such
as copper, lead, cadmium and the presence of organic
contaminants such as polychlorinated biphenyls (PCBs
or dioxins) and “endocrine disrupter” type compounds.
It is important to note that the concentrations
of heavy metal and organic toxins in biosolids have
been declining over the past 20 years because the
discharge of sewage contaminated with metals or
organic toxins from industrial sources is no longer
allowed.
Alkaline (high) soil pH conditions can result from
biosolids treated with lime, especially in soils with low
pH buffering capacity. As with livestock manures,
applications of biosolids to meet N crop needs have
led to buildup of soil P over time. Accordingly,
biosolids and manures share similar concerns related to
non-point source pollution of water bodies