Toxic Culture: All About Toxicity

Determining whether a waste exhibits a hazardous waste characteristic is an important part of the hazardous waste process. (See “Understanding the Four Characteristics of Hazardous Waste for more on this.) The Resource Conservation and Recovery Act (RCRA), which is implemented and enforced by the EPA, establishes hazardous waste requirements across the U.S. Under RCRA, there are four hazardous waste characteristics: ignitability, corrosivity, reactivity and toxicity. Additionally, certain states, including California and Washington, have their own state-specific requirements that expand on the RCRA hazardous waste characteristic definitions. Such state-specific requirements only apply within that state.

Toxicity is the last of the four hazardous waste characteristics. In general, “toxicity” is an attribute of something can cause illness or injury. Health and environmental hazards can be toxic. Specific definitions of “toxic,” however, depend on the circumstances:

  • The OSHA Hazard Communication (HazCom) standard (29 CCFR 1910.1200) includes extensive definitions and classifications of different types of health hazards, which are intended to protect workers who may handle these materials.
  • The U.S. Department of Transportation has a different definition of “toxicity” and different requirements for handling toxic materials, based on the risks these materials pose in transit.

Similarly, there is a specific definition of toxicity for hazardous waste classification purposes based on the potential to cause harm to the environment. Just because a product safety data sheet (SDS) indicates a material has harmful or toxic properties in a workplace safety setting or just because it is regulated as a toxic “hazardous material” when transported, that material is not necessarily considered toxic for hazardous waste disposal.

RCRA hazardous waste toxicity is defined in 40 CFR 261.24 and is based on the potential to cause long-term environmental harm. Only 40 specific substances are regulated:

  • 14 semi-volatile organic compounds (SVOCs)
  • 8 pesticides and herbicides
  • 8 metals
  • 10 volatile organic compounds (VOCs)

A waste exhibits characteristic toxicity if levels of these 40 substances in a representative sample exceed specific thresholds listed in 40 CFR 261.24, Table 1 (“Maximum Concentration of Contaminants for Toxicity Characteristic”) when tested using EPA Method 1311, “Toxicity Characteristic Leaching Procedure” (TCLP). Wastes that exhibit toxic characteristics are assigned a hazardous waste code based on the specific regulated substance or substances: D004–D052. Characteristic wastes may still be “listed” hazardous wastes and carry other F, K, P or U codes.

The TCLP test

RCRA hazardous waste toxicity is based on TCLP, which is a complicated leaching procedure that simulates conditions of wastes if they were to be disposed of in a landfill. Here’s how it works:
  1. A representative sample of the waste is collected. Samples with liquid and solid materials are filtered to separate liquids. If a waste contains less than 0.5% solids, only the filtered liquid needs to be tested, with no extraction.
  2. Remaining solids are mixed with an acidic extraction liquid equal to 20 times the weight of the sample being tested.
  3. This sample and the extraction fluid are actively mixed for at least 18 hours to simulate water seeping through waste in a landfill.
  4. After mixing, the sample/extraction fluid mixture is filtered to remove the solids, and the extraction fluid is combined with any liquid filtered from the original sample.
  5. The combined liquid sample is then analyzed for metals, VOCs or SVOCs, and/or herbicide/pesticides, as applicable.
The results of this analysis determine whether the waste exhibits characteristic toxicity. Wastes that exhibit the characteristic of toxicity are assigned the EPA hazardous waste number specified in Table 1: Maximum Concentration of Contaminants for the Toxicity Characteristic.

The Rule of 20

TCLP values determine whether waste exhibits characteristic toxicity. However, the extraction is complicated, time consuming and relatively expensive. Alternatively, generators can use their knowledge of the “total” amount of hazardous regulated constituents, as well as the 20-times dilution included in the TCLP, to determine a theoretical maximum TCLP result. The total amount of constituent can be based on generator knowledge or derived from separate testing (testing for “total” contaminants is frequently less expensive than TCLP extraction). This approach is sometimes referred to as the “Rule of 20.”

For example, if a generator has a sample of spent bead blast media that may be contaminated with lead-based paint, one option would be to analyze for “total” lead, then divide that result by 20 to determine the theoretical maximum TCLP value:

  • “Total” lead in bead blast media (from separate testing): 80 mg/kg
  • “Total” lead divided by 20, based on TCLP 20:1 dilution (theoretical max TCLP): 4 mg/L
  • Lead TCLP threshold (per 40 CFR 261.24): 5 mg/L

Toxic Culture: All About Toxicity, Part 1

Because the theoretical maximum TCLP results from this sample is 4 mg/L, the TCLP threshold of 5 mg/L cannot be exceeded, and this waste cannot exhibit characteristic toxicity for lead. Some additional things to note:

  • This evaluation assumes 100% of the lead in the contaminated bead blast media is extracted and that the original sample was representative of the overall media blast waste.
  • This is a conservative approach and is likely to overestimate the amount of lead that is extracted. In many cases, only a small percentage of the contaminant actually will be extracted.
  • If “total” analysis showed 120 mg/kg, the theoretical TCLP value would be 6 mg/L. In this case, further testing by TCLP would be required to determine whether the waste does exhibit characteristic toxicity.

As we’ve noted previously, certain states, including California and Washington, have state-specific requirements beyond RCRA hazardous waste characteristic definitions. Look for our upcoming ebook, which will contain expanded content, including state-specific information.

Have any questions about toxic waste or any other hazardous wastes? Please e-mail us at [email protected]. We’re happy to help!

James Kapin is Principal Advisor for safety, health and environmental compliance for ACTenviro.  Jim is a Certified Industrial Hygienist (CIH) and a Certified Safety Professional (CSP) with over 25 years of workplace safety and environmental protection experience.   Do you have any hazardous waste questions for Jim?  Or any other workplace safety or environmental compliance questions?  Let us know at [email protected]

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