Butanamine, N,N-dibutyl-, branched and linear, fluorinated

Endpoint summary

Additional information

PTBA is of very low water solubility (<0.06 µg/L at 23 °C) and is volatile (vapor pressure, 0.02 mm Hg at 20 °C).  An experimental Henry's Law constant (expressed as the ratio of vapor phase partial pressure of PTBA over aqueous phase concentration) of 4.07E+08 Pa∙m³/mol (>4020 atm∙m³/mol) was measured at 22 °C.  A value for log K_OW of 6.1 was determined at 23 °C for PTBA.  However, it is not expected that PTBA will have a significant presence in the aquatic compartment, and bioaccumulation in aquatic organisms is not expected.

 

PTBA is not expected to partition from the atmosphere to moist soils or surface waters.  Based on its uses, PTBA will not be released to aquatic systems or soils.  Upon direct release of PTBA to the aquatic compartment, the chemical would be expected to volatilize rapidly.  However, as noted PTBA release under registered uses is entirely to the atmosphere.  PTBA is not expected to partition to aquatic compartments from the atmosphere, therefore no exposure to aquatic organisms is expected.

 

We have proposed adaptation of the data requirement for bioconcentration factor of PTBA.  Based on a log K_OW of 6.1, the chemical would be considered bioaccumulative in aquatic organisms.  However, substantial bioaccumulation of PTBA in aquatic organisms is not expected due to lack of exposure in aquatic systems.  PTBA is expected to reside entirely in the atmospheric compartment, so air breathing organisms were evaluated for bioaccumulation potential.  According to Chapter R.7.10.3.4 of the Technical Guidance (Other indication of bioaccumulation potential):

 

For air-breathing organisms, respiratory elimination occurs via lipid-air exchange, and such exchange declines as the octanol-air partition coefficient (K_OA) increases, with biomagnification predicted to occur in many mammals at a log K_OA above 5. Such biomagnification does not occur if the substance and its metabolites are rapidly eliminated in urine (i.e. have a log K_OW of around 2 or less). Thus the bioaccumulation potential in air-breathing organisms is a function of both log K_OW and log K_OA. In contrast, respiratory elimination in non-mammalian aquatic organisms occurs via gill ventilation to water, and this process is known to be inversely related to the log K_OW (hence an increase in log K_OW results in a decrease in the rate of elimination and hence increase in the accumulation potential).

 

A log octanol-air partition coefficient (log K_OA) ≤ 0.88. at ca. 23 °C was calculated for PTBA using the relationship:

 

 

K_OA(unitless) = K_OW/ K_AW

 

Where K_OW is octanol:water partition coefficient and K_AW is the dimensionless Henry’s Law constant.  As per Kelly and Gobas⁽¹⁾, chemicals with log K_OA< 4 do not biomagnify regardless of the K_OW because of efficient elimination via air exhalation (or, in this case, extremely inefficient absorption via air inhalation).  According to the classification scheme proposed in Chapter R7.10.3.4, PTBA is a non-polar volatile (high log K_OW and low log K_OA), and is not expected to bioaccumulate in air-breathing organisms.  As stated, the potential to accumulate in aquatic organisms is mitigated by the lack of relevance of the aquatic exposure pathway. Therefore, bioaccumulation of PTBA in terrestrial or aquatic organisms is not expected.

 

Reference:

 

1) Kelly, B.C. and F.A.P.C. Gobas.  2003.  An Arctic Terrestrial Food-Chain Bioaccumulation Model for Persistent Organic Pollutants.  Environ. Sci. Technol Vol. 37, No. 13, pp 2966–2974.