Some deoxyribonucleic acid (DNA) sequencing procedures use trichloroacetic acid (TCA) to determine the tagging efficiency of radioactive phosphorous-32 (32P) to the DNA primers. Typically, all radioactive liquid waste for a laboratory is combined in a single large jug. TCA is a strong acid capable of creating a Resource Conservation and Recovery Act (RCRA) characteristic waste based on pH, even when in low concentration in a waste jug. Volume reduction of mixed waste (RCRA regulated waste combined with radioactive waste) is achievable by segregating the TCA mixed waste from the other radioactive liquid wastes generated in the laboratory.
Applicable Regulations
40 CFR Parts 260-268.

10 CFR 20 Subpart K.

State of Michigan Act 451 Part 111.

Overview of Procedure
During DNA sequencing, some protocols use trichloroacetic acid (TCA) to determine the tagging efficiency of radioactive 32P to DNA segments. TCA is used to rinse a filter under vacuum in order to remove any free (unbound) 32P and leave the labeled DNA segments on the filter paper. The amount of radioactivity on the filter paper compared to the amount of radioactivity in the labeled DNA segments will determine the tagging efficiency. The TCA rinse becomes liquid radioactive mixed waste.

In addition, TCA is a strong acid, capable of creating acidic solutions even when in low concentration in solution. This may create a RCRA characteristic waste (D002) based on pH (see RCRA Overview for more information). Therefore, the TCA rinse will become a mixed waste, both radioactive and RCRA regulated. When combined with other radioactive liquid waste, it can create a large volume of mixed waste.

Waste Minimization Procedure
Segregation of the TCA rinse is the safest and easiest way to minimize the volume of mixed waste generated. A separate liquid radioactive waste container was obtained to hold only the TCA rinses instead of combining the rinses with all the other liquid radioactive waste.

Known Limitations
None known.

Safety & Health Precautions/Personal Protective Equipment
Follow all applicable safety and health protocols and regulations as established by your institution.

Segregation of the TCA rinse reduces the volume of mixed waste generated. This smaller volume is easier to transport and handle safely. In addition, the reduced volume of mixed waste subsequently reduces the disposal costs.

None known.

Project Related Costs
One laboratory using TCA generates approximately 70 gallons of characteristic mixed waste annually. By estimating the amount of TCA rinse used for each procedure and multiplying that figure by the number of times the rinsing procedure is performed, it was possible to estimate that just one gallon of the total 70 gallons of waste was actually mixed waste (TCA combined with 32P). The remaining 69 gallons was low-level radioactive waste only. The low-level aqueous radioactive waste is held for decay-in-storage and subsequently drained to the publicly owned treatment works in accordance with 10 CFR 20 Subpart K.

The disposal costs for one gallon of mixed waste are approximately $158, including the actual disposal cost, analysis, and all personnel time including pickup and paperwork review. Therefore, the disposal costs for 70 gallons of mixed waste would be approximately $11,060.

The disposal costs for one gallon of liquid low-level radioactive waste are approximately $58. Therefore, the disposal costs for 69 gallons of this waste would be $4,002.

The following table illustrates the difference in cost between segregated and non-segregated waste.

Segregated Non-Segregated
1 Gallons Mixed Waste 69 Gallons Low Level Radioactive Waste 70 Gallons Mixed Waste
$158 8,004 11,060
Total Segregated
= $8,162
Total Non-Segregated 
= $11,060

The simple act of segregating this waste stream has the potential to save the U-M approximately $6,900 in disposal costs annually from one laboratory.