A publication of Work On Waste USA, Inc., 82 Judson, Canton, NY 13617 315-379-9200 MARCH 1995
LEAD’S PECULIAR LEACHING BEHAVIOR. The metal that most frequently caused incinerator ash to fail the old EP Tox Test was lead. However, the solubility of lead is highly dependent on the pH of the leaching medium used. The Wheelabrator incinerator in Claremont, NH, was one of the first incinerators in the U.S. to use a lime scrubber as parts of its air pollution control. This lime makes the ash very alkaline. Lead has a peculiar solubility profile as the pH of the leaching medium changes. Lead is highly soluble at a pH of 5 or less. Like most metals, its solubility decreases as the acidity decreases and alkalinity increases. However, unlike many other metals as the pH rises above 11, its solubility begins to rise again. At a pH at or near 12, lead is very soluble. A rough profile of lead’s solubility is illustrated in the diagram on the front page. When excess lime is present in the ash the pH of the solution it generates in water is around 12. Hence the failure for lead when water is used instead of acetic acid in the leachate tests. Conclusion: If an incinerator is using a lime scrubber as part of its air pollution control it is essential to test the ash (especially the fly ash) with water. This, after all, is what it will meet first in the form of rain or melting snow. We can argue about whether distilled water or simulated acid rain should be used in the test, but we need to know how much lead dissolves out of the ash as it gets exposed to the elements. Unfortunately, the TCLP test gives no indication of the impact of rain or melted snow on ash containing lime.
The EPA replaced the EP Tox Text, on March 29, 1990, with the TCLP test. The TCLP test was billed as a more stringent test primarily because it increased the number of pollutants that were examined. However, there was one key difference from the EP Tox Test which has proved highly beneficial to the incinerator industry -- especially for those incinerators which operated with lime scrubbers. That difference was dropping the requirement to reach an acidity of pH 5 in the leaching procedure. Instead, a fixed quantity of dilute acetic acid is added and the pH may end up where it may. In the case of ash which contains high levels of lime, the lime neutralizes most of the added acid and does not allow the leaching solution to reach a pH of 5. The pH ends up between 7 to 10, i.e. where lead is least soluble. The benefit of this change in protocol was spotted early by the incinerator industry. In 1986, David Sussman, V.P. of OGDEN MARTIN stated:
To summarize we can now see what a favor the TCLP test does for an incinerator using a lime scrubber. Both the fly ash and the combined ash (but not the bottom ash alone) would yield a highly alkaline solution with water, with a pH in the range 11.5 to 12.5. Treated with water alone, we would anticipate a high proportion of the lead would be leached out. If this same ash was treated with acid in quantities sufficient to reach a pH of 5 (as in the case of the old EP Tox test) again we would anticipate leaching of lead at higher levels than the 5 mg/liter standard for nearly all the fly ash samples, and about half of the combined ash samples. However, in the TCLP test where only a fixed amount of acetic acid is added, with no concern about reaching a final pH of 5, then the effect of adding the acid is to lower the pH from 12 to a pH of about 7 to 10 -- i.e., in the range of minimum lead solubility. In other words, the TCLP test does not reach the level of acidity where we would expect failure (because the lime neutralizes the acid added), but it does take it away from the high pH (12) where we would expect it to fail the TCLP test if only water was added.
Carol Browner, the head of the US EPA, handed the incinerator industry a huge gift by allowing the incinerator operators to mix the fly ash with the bottom ash prior to testing. The bottom ash contains no lime. A TCLP test applied to this ash alone would probably yield a pH in the acid range and one would anticipate a failure rate of about 30 to 40 percent of the time, as in the case of the old EP Toxicity Tests. However, when the fly ash is mixed with the bottom ash, the lime protects the bottom ash as well. Again, the leaching medium will not reach pH 5, but stay in the range of lead’s least solubility. As bottom ash represents 80 to 90 percent of the total ash, this protection represents a huge financial bonanza to the incineration industry. While the TCLP test serves the industry’s interests, it presents a major threat to human health and the environment.
We have made this decision with the utmost attention to public health...”
Carol Browner, January 25, 1995, in her address to the U.S. Conference of Mayors.
1. The fly ash and the bottom ash should not be combined.
2. The fly ash should be tested daily for total metal content and used as an indicator of the effectiveness of the air pollution control devices.
3. The fly ash should be tested on a monthly basis for its total content of dioxins and furans to see how well the dioxin control strategy is working.
4. The fly ash should be tested with water in a leaching test when the fly ash comes from an incinerator using a lime scrubber (most modern incinerators use lime scrubbers.)
5. The bottom ash should be tested with the EP Toxicity Test to ensure a pH 5 is reached.
6. When a worker begins working at an incinerator or a landfill or driving an ash truck, a blood sample should be taken and stored, should it prove necessary to determine their baseline lead/cadmium and dioxin exposure.
Editors: Ellen & Paul Connett, 82 Judson Street, Canton, New York 13617. Tel: 315-379-9200. Fax: 315-379-0448.