Morpholinium toluene-4-sulphonate

Biodegradation in water: screening tests

Description of key information

Based on all available information the test substance is considered to be readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

The test substance is soluble in water and dissociates to morpholinium and toluene-4 -sulphonate. Since no studies on the ready biodegradability of the substance are available, the biodegradability assessment has been performed with the substance's dissociation products. For this purpose, morpholine and the category of aromatic sulfonic acids which include toluene-4 -sulphonic acid as well as its hydrotropes have been consulted for the evaluation on a read-across approach, respectively.

The biodegradability of morpholine has been examined in a non-GLP guideline study according to OECD 301E with municipal waste water treatment plant effluent as inoculum [BASF AG 1990]. After 28 days a degradation rate of 93 % could be determined. Additional ready and inherent tests are available which confirm that the test substance will be degraded in the environment and as such will not be persistent [BASF AG 1989; BASF AG 1990a; BASF AG 1990b].

Although limited well documented biodegradation studies without clear conclusion on ready biodegradability are available for the biodegradation assessment of aromatic sulphonic acids and specifically toluene-4-sulfonic acid, the conclusion of ready biodegradability is strengthened by the number of supporting literature tests and the fact that seven biodegradation studies are performed with the closely related hydrotropes (the salts) for which it was concluded that these are readily biodegradable. As the cation has a limited affect on the biodegradation potential, and in principle the salt gets dissociated when in contact with water thus forming the acid, it is considered justified to conclude that these substances are readily biodegradable.

Aromatic Sulphonic Acids-

Amongst all the biodegradability studies for the aromatic sulphonic acids, the most reliable study is an OECD guideline study according to 301 D with benzenesulfonic acid (CAS 98-11-3) [Huntsman, 1995a]. The source of the inoculum was a secondary treatment sewage plant. Based on DO measurements, the test substance attained 54% degradation after 28 days which is considered as partly/moderately biodegradable.

Two studies [Pitter, 1976] demonstrate ultimate biodegradability for aromatic sulphonic acids and were conducted with methods similar to OECD guidelines for aerobic activated sludge tests with 28 day duration, reference substances and controls. At the end of the exposure period after 28 days, the author found that benzenesulfonic acid (CAS 98-11-3) and p-toluene sulfonic acid (104-15-4) are biodegradable with degradation rates of 98 % and 94 % in 28 d, respectively.

Two more biodegradation studies are considered in the "weight of evidence". They have relatively little documentation. A 1980 review of MITI tested chemicals reports benzenesulfonic acid (CAS 98-11-3) as biodegradable under aerobic conditions [Kawasaki 1980]. A 1988 study of industrial, adapted activated sludge reports 90% TOC removal for p-toluene sulfonic acid (CAS 104-15-4) [Matsui et al., 1988].

The degradability has been further tested with p-toluene sulfonic acid and non-adapted activated sludge as inoculum. Following a lag period of 50-60 hours and a degredation time of 125 to 135 hours, the substance was found to be 79 - 80 % biodegradable [BUA 1991].

In the OECD test for inherent biodegradability, according to test guideline 302B at a concentration of 720 mg/L p-toluene sulfonic acid monohydrate was eliminated to 95 % after 15 days [BUA 1991], while p-toluene sulfonic acid from the 65-%-aqueous solution at a concentration of 307.5 mg/L was eliminated to almost 100 % after 5 days [BUA 1991]. In another study (Zahn-Wellens Test) p-toluene sulfonic acid monohydrate was degraded to 90 % after 10 days and to 94 % after 20 days while the 65-%-solution was degraded to 75 % after 25 days. When the test with the 65-%-aqueous solution was repeated with an adapted activated sludge, over 90 % degradation was achieved after 10 days [BUA 1991]. Further on, it was shown in another study according to OECD 302B and DIN-Norm 38412 that p-toluene sulfonic acid was degraded by 97 % after a maximum of 12 days incubation, whereby following an adaptation phase of 1 - 3 days, 85 % degradation took place within 5 - 9 days.

In addition, an anaerobic test of aquifer microorganisms showed no biodegradation of benzenesulfonic acid (CAS 98-11-3) in 13 months [Kuhn and Suflita, 1989]. An anaerobic test using a "lab-made sludge", showed no degradation of 100 mg/L of benzenesulfonic acid (CAS 98-11-3), at 37°C for 8 weeks [Kawahara et al., 1999].

While not a microbial toxicity study per se, a 1966 study conducted with 500 mg/L hydroxybenzene sulfonicacid[SS1] , reported inhibition of the microorganisms in the aerobic activated sludge test. However, this study is labeled as "disregarded study" as the 500 mg/L concentration was inhibitory to the microorganisms and there was no biodegradation. OECD guidelines recommend 30 mg/L maximum concentration.

Hydrotropes

Four high quality studies on the biodegradability of the hydrotropes are available which were conducted with the substances sodium xylene sulphonate (CAS 1300-72-7) [Stepan Company 1993; Ruetgers-Nease 1993], sodium cumene sulphonate (CAS 28348-53-0) [Ruetgers-Nease 1993] and sodium toluene sulphonate (CAS 12068-03-0) [Sasol GmbH 2004]. Each of the three substances fulfilled the criteria for ready biodegradability. One study has been conducted with calcium xylene sulphonate (CAS 28088-63-3) [Ruetgers-Nease 1993] which was not considered to be readily biodegradable but biodegradable because it failed the 10 -d-window.

Additionally, two more biodegradation studies with sodium cumene sulphonate [Huntsman 1995] and sodium xylene sulphonate [Huntsman 1995] are available with basic data given. Although the pass levels weren't reached and the 10 -d-window was failed, both test results indicated moderate/partial degradability of the test substances.

Based on all available data on morpholine, the aromatic sulphonic acids and its hydrotropes, the test substance is considered to be readily biodegradable.