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GUEST EDITORIAL NTA-the uncertaintiesremain! The possible wide-scale use of nitrilotriacetic acid (NTA) came under scrutiny at a recent congressional hearing at which industry claimed that reintroduction of NTA was necessary because it represented the only viable alternative detergent builder to sodium tripolyphosphate. Use of NTA in detergents ceased in thc U S . in 1970 at the request of the surgeon general. Since that time, a great deal of experimental work has been undertaken in order to quantify the potential health hazards associated with this material. As with many carcinogenic chemicals, the debate with respect to its use centers upon the level of exposure, if any, that is acceptable from a health risk standpoint. Such considerations take threshold levels into account when attempts are made to relate high dosing rates over short periods of time to long-term dosing at high dilution. With NTA, no such threshold levels have been demonstrated, which is perturbing when considering the possible deliberate introduction of up to a billion pounds of NTA per annum into the water cycle in the U S . Although it is possible to overreact in these circumstances, there are still many factors about NTA's mode of activity in the water cycle that remain unanswered. The environmental case for using NTA rests very heavily upon experiences in countries where NTA is currently being used, such as Canada, Sweden, Holland, and Switzerland. In reality, the only experience lies in Canada because use in the other countries represents, in all cases, less than 1% of the total weight of detergents sold as compared to 15% in Canada. Furthermore, use in Sweden has been decreasing steadily since 1974. In Canada, reported concentrations of NTA in drinking water range from 0.2-24.5 pg/L and average 2.82 pg/L. These figures have been used as the basis of EPA risk assessment, which does not take into account the great differences that occur from country to country. Canada, with. a relatively small population, has abundant water resources and the requirement for water reuse is extremely limited. By comparison with Europe and parts of the U S . , dilutions on effluent
discharge are massive. It can be shown, assuming the same biodegradability data, that NTA levels in certain European rivers would be between two and three orders of magnitude higher than those in Canada if the same detergents were in use. It is claimed that aerobic oxidation of NTA poses very few problems in wastewater treatment. and yet there are surprisingly few data on NTA removal in full-scale Canadian sewage treatment plants. The limited data available relate mainly to areas where high dilutions occur on discharge. Close examination of these data indicates highly variable biodegradation, clearly dependent upon the type of treatment plant and, presumably, variations in temperature and hydraulic loading. The 1978 report of the Great Lakes Research Advisory Board Task Force on the ccological effects of NTA highlighted nine key areas regarding the environmental behavior of NTA where important questions remain, many of which still require detailed investigation. Pcrhaps the two most significant express concern over the possible nondegradability of NTA under anaerobic conditions and the effects on groundwater quality, particularly where septic tanks are involved. Recent work at Imperial College has shown anaerobic NTA degradation to be minimal, so surely the basis of the EPA risk assessment should be reevaluatcd for situations where water reuse is practiced or where groundwater recharge schemes are in operation or being considered. At the commencement of the U.N. decade and at a time when concern about trace organic micropollutants in water is increasing, I find it disturbing that use of NTA could be contemplated on this scale when so many scientific questions arc still unanswered.
0013-936X18110915-0005$01.00/0 @ 1981 American Chemical Society
Roger Perry is head ojrhe Public Health and Warer R ~ . I O U WEngineering ~.C Seccrion a/ rhe Deparlmrnr of C i i i l EngineerinK. Imperial College o/Scknce & Technology. London, U.K. Volume 15. Number 1, January 1981
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