1-hydroxy-4-methyl-6-(2,4,4-trimethylpentyl)pyridin-2(1H)-one, compound with 2-aminoethanol (1:1)

Endpoint summary

Description of key information

ADSORPTIION DESORPTION BEHAVIOUR

[14C]-Octopriox Adsorption Desorption test according OECD 106

As Octopirox exists in an ionic form at higher pH it can sorb not via van der Waal forces but also by ionic interactions (e.g ion pair formation, cation exchange). So far no mechanistic model exists to estimate the sorption behaviour of these substances. Therefore measurements are warranted to address the sorption to solid phases reliably. Sorption was measured in three different soils, one sediment and one secondary sludge. The Freundlich isotherms for the different matrices are non-linear (1/n < 1). As the lowest tested concentration is used for the exposure assessment, Table 5.4-1 below lists the Kd and Koc at that concentration which allows to judge the sorption behaviour without a calculation excerise using the Freundlich isotherm.

  

Table 5.4       Sorption behaviour of [14C]-Octopirox to different solid matrices

 

SOIL		% OC		% Clay		CEC (Meq/100g)	Kd (L/kg) lowest conc.Measured		Koc (L/kg) lowest conc.Measured
Cranfield 164		3.7		28		22.8	4885		132027
Cranfield 277		2.7		57		22.4	4800		177778
Cranfield 299		2.9		26		14.9	4172		143862
mean		3.1		34		15.3	4619		149000
SEDIMENT
SW		6.2		25		21.7	3782		61000
SLUDGE
secondary (activated)		37.5		59		96	1477		3939

 

 The Koc values from the OECD 106 study were used in the Environmental exposure assessment of Octopirox carried out with the EUSES model. As EUSES assigns certain percentages of organic carbon (OC) to the different compartments, Kd values for EUSES were calculate from the available Koc as given in the table 5.4-2

  

Table 5.4-2    Recalculation of Sorption constants for Octopirox to values which can be used in the EUSES Exposure assessment

 

	OECD106 results at 10 µg/L Octopirox		EUSES STANDARD VALUES %OC and Kd related to Koc
SOIL
	% OC	Koc (L/kg) average lowest conc.Measured	% OC EUSES	Kd (L/kg) EUSES based on EUSES OC	EUSES Term for Compartment
Cranfield 164	3.7	132027
Cranfield 277	2.7	177778
Cranfield 299	2.9	143862
mean	3.1	149000 (based on mean values Kd & OC %)	2	2980	SOIL
SEDIMENT
SW	6.2	61000	5	3050	SEDIMENT
SLUDGE
secondary (activated)	37.5	3939	37	1457	ACTIV. SLUDGE

 

Octopirox considerably sorbs to solid matrices especially to soils and sediment.  

Henry’s Law Constant (HLC)

The HLC of the neutral form of Octopirox can be calculated from vapour pressure (IUCLID Section 4.6) water solubility (IUCLID Section 4.8). The Exposure assessment tool EUSES 2.1 recalculates the HLC of 1*E-3 Pa*m3*mol-1at 25 degree C to 4.8*E-4 Pa*m3*mol-1at the environmental temperature of 12 degree C. The dimensionless air-water partitioning coefficient is calculated to 2*E-7 m3/m3. The HLC shows that volatilisation of Octopriox from aqueous solutions is very low.

Measurements of Octopirox in the Influent and the activated Sludge of two Municipal Sewage Treatment Plants (Hanover and Hildesheim, Germany)

Octopirox in activated sewage sludge as well as in the sewage influent of the municipal treatment plants in Hildesheim and Hanvover and was determined in a series of 4 (Hildesheim) and 2 (Hanover) consecutive days. In addition, fortification tests at different levels were carried out.

The analysis of Octopirox from two series of samples confirmed the presence of Octopirox in both sewage influent and sewage sludge. The concentrations measured for two sewage treatment plants were different. Whereas the sewage influent of STP Hannover had lower concentrations of Octopirox, the concentration in activated sewage sludge was higher compared to STP Hildesheim. Octopirox concentration in raw sewage influent of the municipal sewage treatment plant in Hildesheim was in a range of 0.92 – 1.35 µg/l. The concentration of Octopirox in activated sewage sludge was 3.40 – 4.06 mg/kg dw. For the municipal sewage treatment plant in Hannover Octopirox concentration in the raw sewage influent was in a range of 0.30 – 0.55 µg/L and 4.66 – 5.30 mg/kg dw in activated sewage sludge. Recovery rates of the fortification tests confirm the robustness of the analytical method for the determination of Octopirox in raw sewage influent and activated sewage sludge of municipal sewage treatment plants.Details are described in IUCLID Section 5.5.1.

The measured Sewage influent concentrations measured in two Sewage Treatment Plants (Hanover and Hildesheim, Germany) are by a factor of more than 5 lower than estimated by the Exposure Modelling Program EUSES 2.1. The concentrations of Octopirox in the activated Sludge of the STPs are by a factor of more than 6 lower than estimated by EUSES 2.1. One possible explantion could be that Octopirox may have a lower use rate in the area where these STPs are located (compare the Section 9 for estimated Exposure data).