1-nitroguanidine

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

2012-02-12

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Principles of method if other than guideline:

The EPISuite™ QSAR/Property package, as distributed by US EPA, was used for calculation.
EPISuite™ gives two different estimates, based on different types of models. The first estimate is based on a so-called MCI model, a model that uses molecular connectivity indices, parameters that can be derived solely from the 2-D representation (graph) of a molecular structure. Such models usually perform adequately for relatively non-reactive chemicals without highly electronegative or electropositive substituents. The other estimate is based on a correlation of the soil-carbon/water partition coefficient with the octanol/water partition coefficient. Such a model, since it is, preferably, based on a measured property of similar character (viz. KOW), is to be preferred for polar molecules like the guanidines.
However, it is to be expected that, like all amino/amido substances, the guanidines may exist in a protonated form under environmental conditions, depending on their pKa. If so, both the protonated form, and the polar non-protonated form may adsorb to other soil fractions (surface adsorption to charged clay particles e.g.) in addition to partitioning into the soil organic matter fraction. Also, the partitioning behaviour of the protonated form between water and the organic matter fraction may strongly influence the overall partitioning behaviour. No information is available for nitroguanidine.
pKa estimation for nitroguanidine was performed, using SPARC. SPARC estimates a pKa of 10.13 for nitroguanidine.

GLP compliance:

no

Type of method:

other: calculation

Media:

soil

Radiolabelling:

no

Test temperature:

Not applicable

Details on study design: HPLC method:

Not applicable

Analytical monitoring:

not required

Details on sampling:

Not applicable

Details on matrix:

Not applicable

Details on test conditions:

Not applicable

Computational methods:

Not applicable

Key result

Type:

Koc

Value:

4.06 dimensionless

Key result

Type:

log Koc

Value:

0.61 dimensionless

Details on results (HPLC method):

Not applicable

Adsorption and desorption constants:

Not applicable

Recovery of test material:

Not applicable

Concentration of test substance at end of adsorption equilibration period:

Not applicable

Concentration of test substance at end of desorption equilibration period:

Not applicable

Transformation products:

not measured

Details on results (Batch equilibrium method):

Not applicable

Statistics:

Not applicable

Table 1: K_OC values for nitroguanidine, as predicted by EPISuite™

	KOC(L/kg)
	Connectivity Indices model	KP for soil with 10% OM	KOW-based model	KP for soil with 10% OM
Nitroguanidine	20.65	1.15	4.06 (from log KOW(-0.89))	0.22

The most likely K_OC value for nitroguanidine is 4.06 L/kg.

Figure 2: SPARC speciation vs. pH plot for cyanoguanidine > see attached background material

Note that it is the protonated (charged) species that exists predominantly at pH values below the pKa value. It is therefore to be expected that under normal environmental conditions in soil as well as in water (and sediment), nitroguanidine would be present in protonated form. This could well significantly alter its adsorption/desorption behaviour when compared to the predicted behaviour based on the assumption of organic matter partitioning.

Validity criteria fulfilled:

yes

Conclusions:

It can be concluded that nitroguanidine does not adsorb strongly to soil (or sediment). The KOC value derived with EPISuite™, based on the KOW-model, can be considered reliable for both modelling and environmental fate assessments.

Executive summary:

Nitroguanidine is a highly water-soluble, high nitrogen-containing organic substance. The aqueous solubility of nitroguanidine is > 3 g/L (value based on experimental data from this IUCLID5 registration dossier). It is also very hydrophilic, judging by its log octanol-water partition coefficient of -0.89 (also based on experimental data from this IUCLID5 registration dossier). As such, one would suspect that nitroguanidine would not adsorb to organic matter in soil to any appreciable extent. This is confirmed by the estimated KOC value, as presented by the EPISuite™ QSAR/Property package, as distributed by the US EPA. According to the results presented by EPISuite™ it can be concluded that nitroguanidine does not adsorb strongly to soil (or sediment). The KOC value of 4.06 L/kg, derived with EPISuite™, based on the KOW-model, can be considered reliable for both modelling and environmental fate assessments. Additionally, despite the fact that nitroguanidine will be protonated and charged under normal environmental conditions (pKa is predicted to be 10.13), experimental evidence (Haag et al., 1990) clearly shows that nitroguanidine does not adsorb to sediment in a sediment/water adsorption/desorption study.

Description of key information

Experimental information to complete the data requirement for adsorption/desorption screening (REACH Endpoint 9.3.1) are not available. This data requirement is needed to assess the environmental fate of a substance. Therefore, data submission for adsorption/desorption screening for nitroguanidine based on non-experimental methods was provided. According to the results presented by EPISuite™ it can be concluded that nitroguanidine does not adsorb strongly to soil (or sediment). The Koc value derived with EPISuite™ of 4.06 L/kg, based on the Kow-model, can be considered reliable for both modelling and environmental fate assessments.

Key value for chemical safety assessment

Koc at 20 °C:

4.06

Additional information

Adsorption/desorption:

Nitroguanidine is a highly water-soluble, high nitrogen-containing organic substance. The aqueous solubility of nitroguanidine is > 3 g/L. The substance is very hydrophilic, according to its log octanol-water partition coefficient of -0.815. Therefore, it is predicted that Nitroguanidine does not adsorb to organic matter in soil or sediment to any relevant extent. This is confirmed by the KOC value (4.06 L/kg), as estimated by the EPISuite™ QSAR/property package, distributed by the US EPA.

Information on the sediment/water adsorption/desorption behaviour of Nitroguanidine is available. Haag et al. (1990) described an investigation into the environmental fate of nitroguanidine. Among many other parameters, they determined the sediment/water adsorption coefficient of nitroguanidine, using two different sediments, both with a highly specific surface area (a clay and a silt); pH of both sediments was around 7.7, and the organic carbon content was 0.7 % for the clay sediment, and 2.3 % for the silty sediment. Adsorption was determined by establishing the concentration of nitroguanidine in the supernatant water layer before and after equilibration of the aqueous solution of nitroguanidine with sediment.

Haag et al. report a Kp for nitroguanidine for these water/sediment systems of < 0.1, for six concentrations of nitroguanidine, ranging from 1.6 to 6.4 mg/L. Haag et al. also determined the aqueous solubility of nitroguanidine to be 2.6 g/L, and the log Kow as being -0.83. These latter two values are in excellent agreement with the values determined in the key studies of this dossier; the information reported by Haag et al. is therefore considered to be reliable.

The reported Kp for nitroguanidine of < 0.1 for two different sediments with large clay and silt fractions clearly indicate that nitroguanidine, despite its structure and pKa value, does not adsorb to any relevant extent to the inorganic fractions of soils and sediments.

According to the results calculated by EPISuite™ it can be concluded that nitroguanidine does not adsorb strongly to soil (or sediment). The Koc value derived with EPISuite™, based on the Kow-model, can be considered as reliable for both modelling and environmental fate assessments. Any additional information on or testing of adsorption/desorption is not required.