Pyridine, alkyl derivs.

Endpoint summary

Additional information

Environmental Fate

Pyridine, alkyl derivs. is an organic UVCB substance (subtype 2), yellow to dark brown, organic liquid. The composition of the reaction product is variable, thus, several physico-chemical and environmental fate parameters were determined using the model constituent 5-ethyl-2-methylpyridine (MEP, CAS no.: 104-90-5, EC no.: 203-250-0). The read-across between the UVCB substance and the model constituent MEP is justified (see rational for reliability for details).

Pyridine, alkyl derivs. has a density of >= 0.90 to <= 1.10 g/mL. Its physical chemical properties indicate that Pyridine, alkyl derivs. would be expected to be found in water. Pyridine compounds are weak bases that are expected to dissociate in the aquatic environment based on the dissociation constant (Pyridine, alkyl derivs. pKa = 6.6). Released to water bodies with environmentally relevant pH (6-9) a proportion would be present in the cationic (pyridinium ion) form. The vapor pressure is relatively low (vapour pressure for MEP is 1.853 hPa at 20 °C) indicating that Pyridine, alkyl derivs. is slightly to moderately volatile.

Pyridine, alkyl derivs. is considered highly soluble. The water solubility for MEP was determined to be 12 000 mg/L. Notably, most methylated and dimethylated pyridine compounds are miscible in water (Scriven et al 1996). The fact that a significant proportion of the substance is expected to be present in cationic form at ambient pH (6-9) also suggests that its solubility is relatively high. Therefore, while Pyridine alkyl derivs. is expected to be soluble and mobile in the aquatic environment, the extent of solubility will likely depend on the pH of the water and the proportion and nature of the various alkylated pyridine constituents present.

Biodegradation

Pyridine, alkyl derivs. was shown to be inherently biodegradable. In the key study Pyridine, alkyl derivs. was tested according to OECD Guideline 302 C (Inherent Biodegradability: Modified MITI Test (II). After 28 days of exposure, the rate of degradation amounted to 56.6 % when estimated using the ratio BOD/COD. In a supporting study according to OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I)) Pyridine, alkyl derivs. showed limited biodegradation, most likely due to cytotoxicity effects.

In addition to biodegradation studies with Pyridine, alkyl derivs., a ready biodegradation study and a study on inherent biodegradation were carried out using the model constituent MEP. In a study according to OECD Guideline 301 E (Ready biodegradability: Modified OECD Screening Test) MEP was determined ready biodegradable, but failing the 10-day window. In a study according to OECD 302 B (Zahn-Wellens test) MEP showed inherent biodegradation, with 98.7 % degradation in 21 days.

Potential for Bioaccumulation

Pyridine, alkyl derivs. is not likely to bioaccumulate. Based on experimental results obtained using the representative constituent MEP and based on model calculations, Pyridine, alkyl derivs. is considered to have a logPow < 3. Experimental determination of bioaccumulation was waived.

Partition coefficient determination was carried out with MEP. A study according to EU Method A.8, OECD Guideline 117 and EPA OPPTS 830.7570 (Partition Coefficient (n-octanol / water), HPLC Method) revealed a Pow value of 127 and logPow of 2.1 at 22 °C. In a supporting study similar or the partition coefficient was calculated to be logPow 2.39 at 20 °C (Kowwin vl. 67, EPI suite v3.12).

Adsorption/desporption

Testing for adsorption/desorption was waived, as the substance is expected to have a low potential for adsorption (logPow = 2.1 at 22 °C) and the substance decomposes rapidly (inherently biodegradable). The calculated logKoc for model constituent MEP was 2.55 and 2.42 for the MCI and the logKow method, respectively.

Nitrogen-containing aromatic heterocycles such as pyridine compounds are pH-dependent organic cations which adsorb to clay minerals and other negatively charged surfaces in suspension (Ainsworth et al. 1987; Chattopadhyay and Traina 1999; Sims and O’Loughlin 1989). Pyridine and its derivatives often form complexes with metals in aqueous solutions (Yuen et al 1983; Sims and O’Loughlin 1989). Therefore, it is anticipated that the log Koc value of 2.42 - 2.55 modeled for the neutral form of the representative alkylated pyridine structure underestimates its adsorption potential. The cationic nature of the alkylated pyridine constituents of pyridine, alkyl derivs. in surface waters at ambient pHs (6-9) may also expected to attenuate its volatilization potential from water (US EPA 2009). If released to the aquatic environment, Pyridine, alkyl derivs. is expected to reside in the aquatic and to some extent partition into sediment. If released to soil, the water solubility and relatively low logKow of Pyridine, alkyl derivs. suggest low adsorptivity to soil. On the other hand adsorption to mineral surfaces via ionic mechanisms in soil, constitute an important fate process for these substances (Zachara et al 1987). Sorption to mineral surfaces is most likely when the soil solution pH is near or below the compound’s pKa (Sims and O’Loughlin 1989). Notably, volatilization of pyridines can account for up to 57% of the loss from pyridine solutions in soil suspensions (Sims and O’Loughlin 1989, Sims and Sommers 1986)

References

Ainsworth CC, Zachara JM and Schmidt RL 1987. Quinoline sorption on Na-montmorillonite: Contributions of the protonated and neutral species. Clays Clay Minerals 35:121-128

Chattopadhyay S and Traina SJ 1999. Spectroscopic study of sorption of nitrogen heterocyclic compounds on phyllosilicates. Langmuir 15:1634-1639

Scriven EFV, Toomey JE and Murugan R. 1996. Pyridine and Pyridine Derivatives [Internet]. In: Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed. Kroschwitz JI, Howe-Grant M, Eds. New York (NY): John Wiley & Sons. Vol 20. [cited 2010 Aug 11]. Available from: http://www.sciencemadness.org/talk/files.php?pid=90215&aid=2663

Sims GK and O’Loughlin EJ. 1989. Degradation of pyridines in the environment. Critical Reviews in Environmental Control 19(4): 309-340.

Sims GK, Sommers LE. 1986. Biodegradation of pyridine derivatives in soil suspensions. Environ. Toxicol. Chem. 5(6): 503-509.

[US EPA] US Environmental Protection Agency. 2003. Robust summaries of reliable studies for Pyridine and pyridine derivatives HPV category – Appendix A. Available from: www.epa.gov/hpv/pubs/summaries/pyriderv/c14925rs.pdf

[US EPA] US Environmental Protection Agency. 2009. Screening-level hazard characterization: Pyridine and pyridine derivatives category [Internet]. US Environmental Protection Agency [cited 2010 Aug 6]. Available from: http://www.epa.gov/hpvis/hazchar/Category%20Pyr%20and%20Pyr%20Derivs_Sept2009.pdf

Yuen G, Heaster H and Hoggad PE.1983. Amine spectrochemical properties in tris(aminocarboxylate) complexes of chromium(III), Inorg. Chem. Acta., 73, 231

Zachara JM, Ainsworth CC, Cowan CE and Thomas BL 1987. Sorption of binary mixtures of aromatic nitrogen heterocyclic compounds on subsurface materials. Environmental Science Technologies 21:387-402