Registration Dossier

Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

Currently viewing:

Administrative data

Link to relevant study record(s)

Reference
Endpoint:
biodegradation in water and sediment: simulation testing, other
Remarks:
debutylation of the test material by several strains of fungi, yeasts and bacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Not specified
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: No test guideline, No GLP, but peer reviewed and well reported. No purity reported.
Qualifier:
no guideline followed
Principles of method if other than guideline:
The debutylation of the test material by several strains of fungi, yeasts and bacteria to measure biotic biodegradation, and to differentiate between the occurance abiotic and biotic degradation.
GLP compliance:
not specified
Radiolabelling:
no
Oxygen conditions:
aerobic
Inoculum or test system:
other: Sterile water
Duration of test (contact time):
5 d
Initial conc.:
0.01 mg/L
Based on:
test mat.
% Degr.:
6
Parameter:
test mat. analysis
Sampling time:
5 d
Remarks on result:
other: Microorganism: C. globosum
% Degr.:
14
Parameter:
test mat. analysis
Sampling time:
5 d
Remarks on result:
other: Microorganism: Sacch. cerevisiae
% Degr.:
16
Parameter:
test mat. analysis
Sampling time:
5 d
Remarks on result:
other: Microorganism: Ps. fluorescens
% Degr.:
21
Parameter:
test mat. analysis
Sampling time:
5 d
Remarks on result:
other: Microorganism: Sch. pombe
% Degr.:
23
Parameter:
test mat. analysis
Sampling time:
5 d
Remarks on result:
other: Microorganism: A. tamarii
% Degr.:
30
Parameter:
test mat. analysis
Sampling time:
5 d
Remarks on result:
other: Microorganism: Sacch. cerevisiae
% Degr.:
32
Parameter:
test mat. analysis
Sampling time:
5 d
Remarks on result:
other: Microorganism: P. citrinum
Transformation products:
yes
No.:
#1
No.:
#2

The data reported in Tables 3 and 4 have been reduced to percentages of tin in all cases. As expected, the test material has undergone abiotic degradation in all three culture media in the absence of microorganisms under the same conditions as in the bioconversion experiments. Chief degradation products were DBT (1-7 % of the initial TBT) and MBT (3-13 %), with recovery ratios varying from 95 to 115 %.

The results of TBTCl degradation experiments in the presence of microorganisms (Table 3) show that, in all cases, DBT and MBT were obtained either in solution or from the biomass, or both. Moreover; in most-experiments MBT-appears as the major degradation product. The high recoveries (in the range of 100 ± 10%) suggest that only very small amounts of inorganic tin have been formed. Taking into account the non-enzymic conversion allows the calculation of the overall proportion of enzymically transformed TBTCl (Table 3). It is clear that all seven microorganisms have the ability to metabolize TBTCl to various extents ranging from 6 to 32%. However, the partition of the substrate remaining at the end of the reaction, and the resulting metabolites (DBT and MBT), between the solution and the biomass varies widely with the nature of the organotin and the particular microorganism (Table 4). For fungi, TBT and DBT were mainly recovered from the biomass, whereas MBT was mostly in solution. For yeasts and bacteria, there was no apparent trend, except that MBT was recovered almost exclusively from solution. It has not been determined whether the organotins associated with the biomass were adsorbed on the external part of the cells or included within them. It seems likely that the partition of butyltins between solution and biomass is governed, at least in part, by their relative hydrophobic characteristics (cf. the large proportion of monobutyltin in solution).

Validity criteria fulfilled:
not specified
Conclusions:
Biotic degradation of TBT, defined as the difference between overall degradation and abiotic degradation in sterile culture media, was significant after a five-day incubation period at 28 °C for all of the microorganisms studied.
Executive summary:

The debutylation of the test material by several strains of fungi, yeasts and bacteria is described. Under standard conditions and with low initial concentration of substrate, significant biotic degradation of tributyltin (6-32 %) was detected after five days at 28 °C. Dibutyltin and monobutyltin were formed in all cases, with higher yields of the latter. Results suggest that tributyltin biodegradation by microorganisms is generally possible, provided sufficiently low concentrations of substrate are used.

Description of key information

Key value for chemical safety assessment

Additional information

In the Errécalde et al (1995) paper, the debutylation of the test material by several strains of fungi, yeasts and bacteria to measure biotic biodegradation, and to differentiate between the occurance abiotic and biotic degradation were the basic method princples.

A reliability rating of 2 was assigned to this study, according to the criteria of Klimisch, 1997 as no test guideline was specified but the paper was peer reviewed and well reported.

Biotic degradation of the test material, defined as the difference between overall. degradation and abiotic degradation in sterile culture media, was significant after a five-day incubation period at 28 °C for all of the microorganisms studied.

In the Adelman et al (1990) paper, the test material and its degradation products were studied by introducing radiolabeled tributyltin into a 13-m³ marine enclosure (a MERL mesocosm) with near-natural water column and benthos. The test material and its degradation products were monitored for 278 days.

A reliability rating of 4 was assigned to this study, according to the criteria of Klimisch, 1997 as there was no information on GLP status or guideline followed.

The test material lost from marine water via biological degradation at rate of 0.08 day^-1. Two-thirds of degradation to DBT which in turn degraded to MBT at ~0.04 day^-1. One third of TBT degraded directly to MBT. TBT also transported to sediments and volatilised/photodegraded at air-water interface.