Salicylic acid

Biodegradation in water: screening tests

Description of key information

Ready biodegradability: 1 Key study (CITI 1992) performed according to OECD guideline 301C. During 14 days, the biodegradation of salicylic acid at an initial concentration of 100 mg/L was followed. Inoculum used in the test was an activated sludge at a concentration of 30 mg/L obtained by mixing 10 different samples from different city and industrial sewage plants, soils and rivers in Japan. 3 parameters were followed: the Biological Oxygen Demand (BOD), the Total Organic Carbon (TOC) and the test substance analysis (estimated by HPLC). The corresponding percentages of biodegradation obtained after 14 days were 88.1 %, 97.6 % and 100% respectively. Under the test conditions salicylic acid is therefore considered as readily biodegradable. 
Inherent biodegradability: 1 key study (Zahn R. and Wellens H., 1980), performed according to a method which has been later adopted by OECD as the guideline 302B. After 4 days, the biodegradation of salicylic acid, based on the DOC removal, was higher than 90%. Therefore, under these test conditions, Salicylic acid is considered as inherently biodegradable. 
Biodegradability under anaerobic conditions: no key study a weight of evidence approach was prefered (see below).

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Studies are available on the ready and inherent biodegradability in water, and on biodegradability in anerobic conditions.

=> Concerning the ready biodegradability in water, one study (CITI, 1992) has been selected has key study because, although GLP were not mentioned, validity criteria and details on results were not available, this study was performed according to OECD test guideline and was generated by the Japanese Competent Authorities. In this study, during 14 days, the biodegradation of salicylic acid at an initial concentration of 100 mg/L was studied according to OECD guideline 301C. Inoculum used in the test was an activated sludge at a concentration of 30 mg/L obtained by mixing 10 different samples from different city and industrial sewage plants, soils and rivers in Japan. The percentage of biodegradation was estimated by following 3 parameters: the Biological Oxygen Demand (BOD), the Total Organic Carbon (TOC) and the test substance analysis (estimated by HPLC). The corresponding percentages of biodegradation obtained after 14 days were 88.1 %, 97.6 % and 100% respectively. Under the test conditions salicylic acid is therefore considered as readily biodegradable.

Other studies, less described but still validated, support the result obtained in the key study. They can be summarised as follows:

In an OECD guideline 301F test, salicylic acid showed a biodegradation of 94% within 28 days, but no information on the 10-day window criteria were reported (Henschel et al., 1997). In an electrometric respirometric biodegradation test, salicylic acid was ranked as “easily biodegradable” by the authors (Urano K and Kato Z, 1986).

Other supporting studies, considered as less reliable due to lack of data, are not reported here.

=> Concerning the inherent biodegradability profile of salicylic acid, one study (Zahn R. and Wellens H., 1980), performed according to a method which has been later adopted by OECD as the guideline 302B, has been selected as key study. After 4 days, the biodegradation of salicylic acid, based on the DOC removal, was higher than 90%. Therefore, under these test conditions, Salicylic acid is considered as inherently biodegradable.

Other studies, less described but still validated, support the result obtained in the key study.

One study (Dore etal., 1975) reported measurement of Chemical Oxygen Demand and Biological Oxygen Demand for 5 days performed according to French AFNOR NF methods. The results obtained for the salicylic acid were a COD equal to 100 % of ThOD and a BOD5 equal to 41 % of ThOD. Considering that the ratio BOD5/COD is below 0.5, salicylic acid can not be considered as readily biodegradable in this study. This result is in contradiction with the previous results from KS and SS. However, the present results from BOD5 must be considered with care because they are susceptible to many parameters, particularly to the adaptation of the microflora which determines the lag phase, parameter which is not mentionned in this study. Therefore it may be possible that the inoculum was not adapted and therefore lag phase was longer and the short exposure time was not sufficient to observe the biodegradation.

=> Studies are available on the biodegradability in water under anaerobic conditions. These studies were not considered of sufficient validity to select a key study. Instead, a weight of evidence approach is considered. In different testing conditions, the biodegradability observed ranged from 75% to 85%; therefore, it can be concluded that salicylic acid can be degraded under anaerobic conditions.