A possible flaw in EPA's 1993 new sludge rule due to heavy metal interactions

Abstract

The new 1993 sludge rule of the EPA (Environmental Protection Agency) sets (a) concentration limits for ten different heavy metals in sludge or sludge products that are sold or given away for use on soil, (b) cumulative loading rates for those ten metals in soil, (c) concentrations of the metals that can be considered as “clean” sludge, and (d) annual loading rates that must be met if the sludge is not “clean” but below the ceiling concentrations. The rule allows for widespread liberal use if the pathogen aspects are complied with. This encourages addition of organic carbon to soils which is urgently needed for soil improvement. The permissible levels of heavy metals may be too high, however, because EPA obviously did not fully consider the interactions which occur when 2–3–4–5 or more heavy metals are at high levels simultaneously especially after 40 years of use when decomposition releases some of the heavy metals. We have observed field situations where use of sludge composts for as many as 40 years have led to heavy metal toxicities particularly for Cu and Zn and with soil pH that is very acid.