Bis(tributyltin) oxide

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

not reported

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA OPP 165-4 (Laboratory Studies of Pesticide Accumulation in Fish)

GLP compliance:

yes

Radiolabelling:

yes

Details on sampling:

- Sample storage conditions before analysis: Samples were stored at -20 °C in the dark
- Details on sampling and analysis of test organisms: Fish while still partially frozen are rinsed with reagent water to remove extraneous material. Edible portions of the fish were dissected under contaminant free conditions. Sufficient tissue was pooled in a combusted mason jar and macerated using a Tizzumizer or Polytron Blender. The macerated tissue was then weighed into a centrifuge bottle (2-15 g wet weight). The moisture content (percent) is determined using 5 g samples of macerated tissue. The remaining pooled tissue samples are serially extracted with 0.2% tropolone in methylene chloride using a Tissumizer. The extracts are then hexylated with Gringard reagent. A silica/alumina column cleanup step is used before the instrumental analysis to remove matrix interferences. The extract is then submitted for analyis of butyltins.

Vehicle:

no

Test organisms (species):

Lepomis macrochirus

Details on test organisms:

TEST ORGANISM
- Common name: Bluegill sunfish
- Strain: Lepomis macrochirus
- Source: Osage Catfisheries Inc. Osage Beach, Missouri

Route of exposure:

aqueous

Test type:

flow-through

Water / sediment media type:

natural water: freshwater

Total exposure / uptake duration:

28 d

Total depuration duration:

21 d

Hardness:

Not reported

Test temperature:

Not reported

pH:

Not reported

Dissolved oxygen:

Not reported

TOC:

Not reported

Details on test conditions:

Not reported

Nominal and measured concentrations:

0.076, 0.072, <0.0095 ppb, TBT as Sn

Reference substance (positive control):

not specified

Details on estimation of bioconcentration:

The TBT bluegill BCF study consisted of two parts: 1) an evaluation of radiolabeled TBT uptake to steady state depuration, and 2) an analysis of butyltin metabolites of TBT.

Juvenile bluegill were exposed to 0.072 ug Sn/L (0.18 ug TBT/L) for 28 days in a flow-through system. the uptake phase consisted of 28 days of continuous exposure. The depuration phase began on day 29 and continued for a total of 21 days. Fish were sampled at days 21 and 28 (uptake phase) and day 21 (depuration phase). TBT and butyltin metabolites were measured in fillet and viscera.

Type:

BCF

Value:

700

Basis:

edible fraction

Calculation basis:

steady state

Remarks on result:

other: Uptake 21 days

Remarks:

Conc.in environment / dose:0.76 ppb

Type:

BCF

Value:

1 050

Basis:

non-edible fraction

Calculation basis:

steady state

Remarks on result:

other: 21 days uptake

Remarks:

Conc.in environment / dose:0.76 ppb

Type:

BCF

Value:

900

Basis:

edible fraction

Calculation basis:

steady state

Remarks on result:

other: 28 days uptake

Remarks:

Conc.in environment / dose:0.072 ppb

Type:

BCF

Value:

1 310

Basis:

non-edible fraction

Calculation basis:

steady state

Remarks on result:

other: 28 days uptake

Remarks:

Conc.in environment / dose:0.072 ppb

Details on kinetic parameters:

- Depuration: Linear half-lives for TBT based on fillet and viscera samples were calculated using method 1 to be 18 and 14 days, respectively. Similar half-lives were calculated using the exponential method. TBT half-lives calculated using method 2 were 17 and 10 days, for fillet and viscera, respectively

Metabolites:

Tissue TBT/DBT ratios in fillet samples ranged from 5.3 to 8.7, while viscera samples exhibited TBT/DBT ratios of 1.8 to 2.7. This suggests that viscera, probably the liver, was a more active site for TBT degradation than fillet tissue. Ratios decreased within fillet and viscera samples from day 21 uptake to day 28 uptake to day 21 depuration. The observation of decreasing TBT/DBT ratios through time supports the hypothesis of in-vivo TBT degradation and progressive induction of enzymes capable of degrading TBT. It is also conceivable that tissue DBT residues reflected some degree of bioconcentration from the water during the uptake phase.
Bluegill tissue concentrations of monobutyltin were detected in only three of six treatment samples. Maximum MBT concentrations measured in tissue were less than four times the detection limit of 5 ng Sn/g dry weight. Results indicate a three to four week lag time between TBT uptake and appearance of MBT in fillet. Equally important, MBT depuration was sufficiently rapid so that MBT was not detected in any depuration sample.

Details on results:

Not reported

Reported statistics:

The half-life of TBT in the bluegill tissues was calculated using two methods. Because of limited data, the TBT degradation curve could not be defined. Therefore, TBT degradation was determined using two assumptions: 1) the TBT degradation curve is linear (method 1), and 2) the curve is exponential (method 2).
Method 1 is presented below:
1) Calculate change in TBT tissue concentration (i.e., A TBT) from steady State (day 28 of uptake phase) to day 21 of depuration phase.
2) Calculate change in TBT per day (A TBT/day) by dividing A TBT by number of days between sampling (21).
3) Calculate 50% of steady State TBT tissue concentration.
4) Linear half-life is computed by dividing 50% steady State TBT tissue concentration by A TBT/day.
The exponential first order method, or method 2 (e.g., Eggers, et al., 1964) for calculating half-lives is presented below:

T1/2 = 0.6931 x t/(ln(Co/Ct))

where T1/2 = half-life, exponential
t = time, in days, from steady State to end of depuration
In = natural log
Co = Conc. TBT at steady State (tissue)
et = Conc. TBT at day 21 depuration (tissue)
0.6931 = In 2 (constant)

Tissues of test fish that were previously exposed to aqueous radiolabeled ¹⁴C-Bis(tri-nbutyltin) Oxide (TBTO) were analyzed for tetrabutyltin, tributyltin, dibutyltin, and monobutyltin. No control samples (0 of 6) contained detectable concentrations of butyltins. Zero of six treatment samples contained detectable concentrations of TTBT, while MBT was detected in three of six treatment samples at concentrations not exceeding four times the detection limit of 5 ng Sn/g dry wt. Tributyltin (TBT) and dibutyltin (DBT) were detected in all six treatment tissue samples. These samples included uptake (days 21 and 28) and depuration (day 21) phases and both fillet (edible tissue) and viscera. Highest TBT concentrations were found in day 28 uptake viscera samples (94.4ngSn/g wet wt.), associated with a mean TBT (as Sn) exposure concentration of 0.072 ng Sn/L. Decreases in tissue TBT concentrations after 21 days of depuration were approximately 58% (fillet) and 76% (viscera) of residues at 28 days of the uptake phase.

 

Dibutyltin concentrations in the six tissue samples followed a similar pattern, with highest values observed on day 28 of the uptake phase samples in viscera (37.8 ng Sn/g wet wt.). The mean TBT exposure concentration in the water was 0.072 ng Sn/l, and the mean aqueous DBT concentration was 0.04 ng Sn/L. Samples collected on day 21 of the depuration phase yielded tissue DBT concentrations that were a fraction of day 28 uptake phase samples. The day 21 depuration fillet sample revealed a decrease in DBT concentration of approximately 47 percent compared to the day 28 uptake value. The day 21 depuration sample of viscera revealed a decrease in DBT concentration of approximately 66 percent from the day 28 uptake phase sample.

Validity criteria fulfilled:

not specified

Conclusions:

Steady state TBT bioconcentration factors (BCFs) ranged from 700 to 900 in fillet and 1050 to 1310 in viscera of juvenile bluegill in aqueous exposure. Tissue TBT concentrations were consistently higher in viscera samples vs. fillet samples. On day 28 of the uptake phase, TBT concentrations always exceeded those measured on day 21 (uptake) and day 21 (depuration).

Executive summary:

Aqueous exposure of bluegill sunfish to TBT resulted in measurable TBT uptake by test fish. Both fillet and viscera revealed TBT residues that exceeded exposure conncentrations. BCFs ranged from 700 to 900 in fillet and from 1050 to 1310 for viscera.

Description of key information

Steady state TBT bioconcentration factors (BCFs) ranged from 700 to 900 in fillet and 1050 to 1310 in viscera of juvenile bluegill in aqueous exposure. Tissue TBT concentrations were consistently higher in viscera samples vs. fillet samples. On day 28 of the uptake phase, TBT concentrations always exceeded those measured on day 21 (uptake) and day 21 (depuration).

Key value for chemical safety assessment

BCF (aquatic species):

2 210 dimensionless

Additional information

The key study for this endpoint Gendusa, T.C., and Brancato, M.S. (1991) was performed in compliance with GLP and to the guideline EPA OPP 165-4 (Laboratory Studies of Pesticide Accumulation in Fish). As such the study was considered relaible for assessment and awarded a reliability score of 1.