Iodine

Monitoring data

Administrative data

Endpoint:

monitoring data

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

publication

Title:

The determination and monitoring of 131I activity in sewage treatment plants based on A2/O processes

Author:

Fernando Jiménez, Raúl López, Rafael Pardo, Luis Debán, Marta García-Talavera

Year:

2011

Bibliographic source:

Radiation Measurements Volume 46, Issue 1, January 2011, Pages 104-108

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The 131I activity was determined based on its precipitation as silver (I) iodide, its dissolution with cyanide in ammonia medium and its measurement by the liquid scintillation counting technique (LSC).

GLP compliance:

no

Media:

other: wastewater

Study design

Details on sampling:

Inlet and treated water samples were collected at the STP of Valladolid (Spain) during the year 2006. The depurating process of the STP consists of decantation, biological treatment using an A2O (anaerobic, anoxic and oxic conditions) process, decantation and spill into the PisuergaRiver. Inlet water samples were collected just before the first decantation whereas effluents were collected just before spilling into the river. Samples were kept in polyethylene bottles, cooled during transport and immediately analyzed.

Results and discussion

Any other information on results incl. tables

The maximum 131I activity found in the influents was 2.6 Bq/kg.

 

The removing or depurating efficiencies calculated as the ratio between the values of paired treated and inlet water samples for 131I was between 25 and 93% with a mean value of 52%.

The correlation matrix of the depurating efficiencies show that the existence of significant correlations amongst COD, BOD5 and SS (p < 0.05) and the lack of correlation between all of them with the 131I removing efficiency (p > 0.05).

Applicant's summary and conclusion

Conclusions:

A procedure for the determination of 131I activity in wastewater based on the LSC measurement of a chemically treated sample has been proposed and optimized. Under the optimized conditions, LSC allows the determination of 131I activities with a detection limit (CCβ) of 11.0 mBq/kg.
The STP reaches a mean 131I removal efficiency of 51.6%, and no conclusive pathway for the elimination of 131I during the depuration process were found.

Executive summary:

A procedure for the determination of 131I activity in wastewater based on the LSC measurement of a chemically treated sample has been proposed and optimized. The LSC procedure has been validated by comparison with ISO standard gamma spectrometry giving comparable results. The main advantages of LSC against gamma spectrometry are (1) a smaller sample volume is needed (1 L vs. 20 L), (2) smaller counting time (13 h vs. up to 48 h) and (3) several samples can be simultaneously processed. Under the optimized conditions, LSC allows the determination of 131I activities with a detection limit (CCβ) of 11.0 mBq/kg.

The LSC procedure has been applied to the determination of 131I activity in the inlet as well as treated wastewater of the STP in Valladolid (Spain). All analyzed samples were below the allowed limits, and the annual evolution of 131I activity in the non-treated wastewater shows a near constant background activity and some sharp increases corresponding to authorized spills from hospital facilities. The STP reaches a mean 131I removal efficiency of 51.6%, and no conclusive pathway for the elimination of 131I during the depuration process were found.