Microtox (TM) characterization of foundry sand residuals

Although foundry residuals, consisting mostly of waste sands, represent a p otentially attractive, high-volume resource for beneficial reuse applicatio ns (e.g. highway embankment construction), prospective end users are unders tandably concerned about unforeseen liabilities stemming from the use of th ese residuals. This paper, therefore, focuses on the innovative use of a mi crobial bioassay as a means of developing a characterization of environment al suitability extending beyond the analytical coverage already provided by mandated chemical-specific tests (i.e., TCLP, etc.). Microtox(TM) bioassay s were conducted on leachates derived from residuals obtained at a wide ran ge of facilities, including: 11 gray and ductile iron foundries plus one ea ch steel and aluminum foundries. In addition, virgin sand samples were used to establish a relative 'natural' benchmark against which the waste foundr y sands could then be compared in terms of their apparent quality. These bi oassay tests were able to effectively 'fingerprint' those residuals whose b ioassay behavior was comparable to that of virgin materials. In fact, the m ajority of gray and ductile iron foundry residuals tested during this repor ted study elicited Microtox(R) response levels which fell within or below t he virgin sand response range, consequently providing another quantifiable layer of support for this industry's claim that their sands are 'cleaner th an dirt.' However, negative Microtox(TM) responses beyond that of the virgi n sands were observed with a number of foundry samples (i.e. four of the 11 gray or ductile iron sands plus both non-iron sands). Therefore, the latte r results would suggest that these latter residuals be excluded from benefi cial reuse for the immediate future, at least until the cause and nature of this negative response has been further identified. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.