Trisodium nitrilotriacetate

Field studies

Administrative data

Endpoint:

field studies

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Meets generally accepted scientific standards, well documented and acceptable for assessment.

Cross-reference

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1974

Materials and methods

Principles of method if other than guideline:

Field studies of NTA degradation were undertaken downstream of a Canadian activated sludge waterwater treatment plant in summer and winter and at two different NTA input levels to compare the relative efficiency at different temperatures. Sampling was undertaken at six locations over a 5 mile stretch of river downstream of the plant. Temperature, and stream flow were routinely monitored. Fluorometric tracer studies were simultaneously undertaken to evaluate the mixing properties of the stream.

Additional simulation tests were carried out on a water and sediment system taken from the river and subjected to four different temperature regimes. The results of these is reported under 5.2.2 Biodegradation: Simulation Testing.

GLP compliance:

no

Type of measurement:

Test substance concentration

Media:

Freshwater

Test material

Test material information

Constituent 1

Reference substance name:

nitrilotriacetic acid (NTA)

IUPAC Name:

nitrilotriacetic acid (NTA)

Details on test material:

- Name of test material (as cited in study report): NTA
- Source: not provided
- Analytical purity: not provided
- Na3NTA.H2O weighed to give required H3NTA concentration

Results and discussion

Any other information on results incl. tables

FIELD STUDIES - NTA REMOVAL IN WWTP AND DOWNSTREAM - EFFECT OF TEMPERATURE
- The degradation of NTA in the natural river environment downstream of a wastewater treatment plant with NTA input at two NTA input levels (16 -20 mg/L and 8 -16 mg/L) in winter and summer. Samples were taken from six points along a five mile stretch of river. Fluorometic tracer studies were undertken to evaluate the mixing properties of the stream.
- During summer (aeration tank 13 -14.5 C, stream 16.5 -21 C), NTA removal by the treatment works was >95% and the effects of dilution and degradation gave downstream NTA concentrations of less than 10 microg/L.
- In winter (aeration tank 10 C, stream 0.5 -3.0 C), NTA removal by the plant was <45%, and downstream NTA concentration peaked at 125 microg/L. There was evidence of in-stream biodegradation even at the lower temperatures.

Table - Average NTA Concentration in Grindstone Creek in µg/L

Location	Period
	Summer	Summer	Winter	Winter
	Low-NTA	High-NTA	Low-NTA	High-NTA
Plant: Influent	8000	22200	8340	20500
Plant: Effluent (site 1)	355	932	5370	11735
End of Tributary (site 2)	278	645	5590	8609
Downstream from tributary (site 3)	--	--	73	106
Highway 403 overpass (site 4)	<10	<10	27	68
Lamb’s Hollow (site 5)	<10	<10	32	42
Highway 2 overpass (site 6)	<10	<10	30	52
Hamilton Harbour (site 7)	--	--	33	55
Aeration Tank Temperature (ºC)	13.0	14.5	10.0	10.0
Stream Temperature (ºC)	16.5	21.0	0.5	3.0

FIELD STUDIES - DEGRADATION PRODUCTS/PATHWAYS
- Waterdown waterwater treatment works processes domestic wastes, therefore metal concentrations from plant effluent were relatively low., limiting the formation of NTA-metal complexes. Therefore, the majority of the NTA leaving the plant as effluent would be either uncomplexed, or as calcium or magnesium complexes (rapidly biodegradable forms).
- The authors considered it unlikely that resistant heavy metal complexes contributed significantly to the degradation of NTA in Grindstone Creek. However, the formation of NTA-metal complexes may contribute to the degradation pathway of effluent from treatment plants handling industrial waterwaters.

Applicant's summary and conclusion

Conclusions:

In summary, the effect of temperature (18, 12, 7 and 2 C) upon biodegradation of NTA in a simulated freshwater/sediment system was evaluated. Biodegradation was found to occur even at very low temperatures (albeit at a low rate). First order degradation rate coefficients were determined as 0.036/H at 18 C and 0.006/H at 2 C. NTA was found to degrade in freshwaters at low temperature and was readily biodegradable at temperatures over 10 C. The author concludes NTA buildup in receiving waters from the wastewater plant was unlikely to occur.

Executive summary:

Field studies were undertaken to assesses the degradation of NTA in the natural river environment downstream of a wastewater treatment plant with NTA input at two NTA input levels (16-20 mg/L and 8-16 mg/L) in winter and summer. NTA removal by the treatment works at 13-14ºC (aeration tank temperature) was >95% compared to <45% at 10ºC. The effects of dilution and degradation gave downstream NTA concentrations of less than 10 µg/L at higher temperatures (16.5-21ºC), and 125 µg/L at lower temperatures (0.5-3.0ºC). Levels of NTA it the mouth of Grindstone Creek averaged 40 -50 µg/L at the time of the study. There was evidence of in-stream biodegradation even at the lower temperatures. Whilst dilution and dispersion were obviously major factors in removal of NTA from the system, downstream observed NTA concentrations were found to be lower than expected from these processes alone, suggesting (together with the temperature effects) that in-stream biodegradation had occurred.

Waterdown wastewater treatment works processes domestic wastes, therefore metal concentrations from plant effluent were relatively low, limiting the formation of NTA-metal complexes. Therefore, the majority of the NTA leaving the plant as effluent would be either uncomplexed, or as calcium or magnesium complexes (rapidly biodegradable forms). The authors considered it unlikely that resistant heavy metal complexes contributed significantly to the degradation of NTA in Grindstone Creek. However, the formation of NTA-metal complexes may contribute to the degradation pathway of effluent from treatment plants handling industrial wastewaters.