Ethidium Bromide (EtBr) is an intercalating stain frequently used by molecular biologists for visualization of Deoxyribonucleic acid (DNA) in agarose gels. EtBr is widely used by many researchers due to its high sensitivity, rapid staining, and very inexpensive price. Unfortunately EtBr is a powerful mutagen; hence there are concerns about its use and ultimate disposal. The reduction of this hazardous substance in the wastestream may be possible with the implementation of on-site EtBr filtration systems and/or substitution of less toxic alternatives.*
Applicable Regulations
State of Michigan Act 451 Part 121.

Overview of Procedure
EtBr is a commonly used stain by the molecular biological community. The stain is versatile and typically used for several different staining applications, thus adding to the frequency of use and subsequent volume of waste produced. Currently, EtBr waste solutions are collected and sent for disposal by incineration with one of the University of Michigan's (U-M) chemical waste vendors.

More sensitive, less toxic alternative stains are still being researched. In the meantime, a pilot study to assess the viability of EtBr extractors for handling this waste stream is being performed. The EtBr extractor houses a specially formulated activated carbon matrix disk for the adsorption of EtBr. Each extractor is capable of filtering up to 10 liters of EtBr contaminated solution at a concentration of 0.5g/mL.

Waste Minimization Procedure
Attach the EtBr extractor to a vacuum source via 1/4 1/2" vacuum tubing. Place a waste container under the extractor, making sure the extractor fits securely on top of the waste container that the waste solution is to be filtered into. Remove the cover of the extractor; apply vacuum while holding the unit. The solution may now be poured through the extractor. If the solution is viscous or partially gelled, a five percent urea solution may be added to dissolve gel.

* Note for University of Michigan Laboratories: Any liquid or solid waste generated, even if filtered through EtBr extractor, must be collected by OSEH Hazardous Materials Management. For more details or to schedule a pick-up, please call 763-4568.

Known Limitations
EtBr extractors may only be used with aqueous solutions of EtBr waste; organic solvents readily break down the matrix of the filter rendering it useless.

Filters tend to clog over extended periods of time due to agarose from gels.

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

The main benefit from the use of EtBr extractors is elimination of the liquid EtBr waste stream and hence a savings on disposal costs. The EtBr impregnated filters are disposed of as a solid waste at a reduced cost.

There are no known disadvantages to using EtBr extractors.

Project Related Costs
The cost to dispose of EtBr at the U-M (1996) is as follows:

(902 liters) @ ($5.00/liter) = $4,510

(3233 lbs.) @ ($2.50/lb) = $8,082

The EtBr extractor systems cost $7.13 per unit, have a filtration capacity of 10 liters, and a 99 percent removal efficiency. An overall filtration price would be $0.71/liter. A minimum order of 72 units is required to receive the discounted price of $7.13 per unit.

The extractor units weigh 84 grams (0.168 lbs.) each. Weight difference is negligible between used and unused filters.

The figures reflect an optimum concentration of 0.5 mg/L. Concentrations used by U-M researchers are typically in the range of 0.05 to 0.1 mg/L, hence increasing the actual volume that could be filtered and lowering the cost per liter estimate.

Using the disposal information from 1996 an analysis can be made as to how much the U-M would have saved with the use of the EtBr extractors:

Current Cost of the EtBr Disposal:
Disposal Cost for solid EtBr waste: $8,082.50

Disposal Cost for liquid EtBr waste: $4,510

Total Actual Disposal Cost for 1996: $4510 + $8,082.50 = $12,000

If EtBr Extractors Had Been Used:
(902 L) (10 L/filter) = 90.2 or 91 filters needed

Purchasing Cost of Filters:
(91 filters) X ($7.13/filter) = $637

(91 filters) X (0.168 lbs./filter) = 15.3 or 16 lbs. of additional solid waste

16 lbs. + 3,233 lbs.:
3,249 lbs. total solid waste

(3,249 lbs.) X ($2.50/lb):
$8,122.50 adjusted disposal cost for solids.

Total Cost if Filters Had Been Used:
$637 + $8,122.50 = $8,759

Theoretical Cost Savings:
$12,592.50 - $8,759 = $3,833