ISPHORDING, WAYNE C., University of South Alabama, Mobile, AL; and MARIA E. BUNDY, Louisiana State University, Baton Rouge, LA
Abstract: The Dilemma of Assessing Heavy Metal Toxicity
Geologists must often determine the degree to which a site is contaminated by heavy metals. It is critical to understand that it is not the total quantity of a metal that determines toxicity but rather the bioavailable amount that is of concern. Soils near industrial and drilling sites may well contain elevated quantities of heavy metals. Standard practice is to perform a Toxicity Characteristic Leaching Procedure (TCLP) and if metals are found in excess of EPA limits, a "clean up" is mandated. Industries spend millions of dollars treating such soils because they believe that there is no alternative action. The EPA will consider exceptions, appeals procedures are available. To appeal, information must be supplied to show why an exception should be granted. The strongest argument is that quantities indicated by the TCLP do not reflect the amounts potentially releasable at a site or that the metals are in a "safe" form. The TCLP is a flawed procedure. The EPA is well aware that the TCLP does not always produce reliable results. Identifying the quantity of a metal that can be leached from a soil and rendered bioavailable requires tests to be performed under site ambient conditions. The TCLP extracts the metal at a pH of 4.93 (or 2.88). Rarely are conditions at the site at either of these pH's Further, it is critical to know the manner by which the metal is held in the soil. A TCLP, in no way, identifies the amount of a metal held in organic, reduced, oxide, or structural phases. These strongly control actual bioavailability and toxicity. To determine this, selective ion site partitioning analysis is needed. It is this information that may then be useful (or critical) in an appeal process. Three examples are given where clean up operations based upon TCLP results would have been inappropriate and would have incorrectly addressed actual environmental problems at the sites. These include bottom sediments proximal to oil drilling operation near the mouth of Mobile Bay, Alabama, a reservoir in Alabama surrounded by abandoned coal mine dumps, and a wetland area adjacent to a refinery in Louisiana.
AAPG Search and Discovery Article #90924©1999 GCAGS Annual Meeting Lafayette, Louisiana