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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Administrative data

Link to relevant study record(s)

Description of key information

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

HCAT is a complex with molybdenum bound to 2-EHA (2 ethylhexanoic acid) molecules; there is also some unbound 2-EHA in HCAT (<=11%).

HCAT is a Class 1 Sensitiser, produces Category 1 eye irritation. HCAT is also classified as a Category 2 reproductive toxin due to the effects of 2-EHA which is a major impurity and breakdown product of the complex. Appropriate personal protective clothing will be mandatory to minimise human exposure. Additionally, HCAT will only be transferred from/to vessels/large containers at dedicated facilities (PROC 8b) and used in a closed process with no likelihood of human exposure (PROC 1). During its use as a processing aid, the HCAT complex dissociates and the liberated molybdenum forms molybdenum sulphide (sulphur scavenging), and 2-EHA acid is decarboxylated to 2-ethylpentane.

Worker exposure to HCAT is therefore limited to the process of transferring the stainless steel hosing from an empty ISO tanker to a full ISO Tanker, where there may be residual HCAT located on the internal hose fitting, and during depressurization of the empty ISO Tanker, where nitrogen and residual HCAT may be expelled upwards into the air. This process is conducted at most every 21 days and each procedure lasts for <15 min.

Any exposure is therefore more likely to occur from 2 -EHA impurity rather than from HCAT itself, which is a large organometallic complex with a limited ability to be absorbed across membranes (molecular weight 1296 g/mol). For Classification & Labelling purposes, a consideration of the toxicokinetics of 2-EHA is therefore considered.

Available Toxicokinetic Data for 2-EHA

The ECHA Substance Information Database refers to a 1987 report on the toxicokinetics of 2-EHA in rats. Details are limited, but a Klimisch score of 2 has been assigned. The key features of the studies were:

• Acute gavage doses of 100 and 1000 mg/kg;

• Gavage dosing, once daily for 15 days at 100 mg/kg/day;

• Acute intravenous dose of 1 mg/kg;

• Dermal (96 hours occluded) dosing at 100 and 1000 mg/kg;

• Blood sampling at the lowest dose for each dose route only, up to 96 hours post dose;

• Urine collection over 96 hours.

When 100 mg/kg/day (exceeding the NOAEL in the 90 day toxicity study) was given orally, most of the dose was excreted within 24 hours, and in a tri-phasic manner; the half-lives were approximately 0.2, 6.6 and 117 hours. A similar triphasic excretion pattern applied with intravenous dosing (half lives approximately 0.3, 6.8 and 98 hours). With dermal dosing, the peak level was observed approximately 5.7 hours after application, with absorption half-life of approximately 3.2 hours. A biphasic excretion was observed, with half-lives approximately 4.2 and 251 hours. It is considered that the 2 excretion phases after dermal application probably corresponded to the second and third excretion phases after gavage or intravenous dosing; the initial excretion phase after gavage or intravenous dosing would be expected to be too short to detect with the slow absorption after dermal application.

Approximately 75% of the dose was excreted in the urine, but after 100 mg/kg by gavage 50% was excreted within 8 hours, compared with only 20% excreted at 1000 mg/kg. This shows a more rapid excretion (as a proportion of dose administered) with lower doses. For HCAT, where exposure is likely to be minimal, any human dose would be small and therefore would be predicted to be excreted rapidly.

Analysis of the urine showed that the 2-EHA was excreted either unchanged, as the glucuronide, or a glucuronide conjugate of hydroxylated and diacid derivatives of 2-ethylhexanoic acid. Kröger et al (Int Arch Occup Environ Health. 1990; 62(3):213-6) have shown that sawmill workers exposed to 2-EHA tend to excrete the 2-EHA in the urine.

Available toxicokinetic data for molybdenum

The REACH Registration Dossiers for molybdenum compounds shows that for the purpose of human health risk assessment, the substances sodium molybdate, ammonium octamolybdate, molybdenum trioxide and roasted molybdenum concentrate are considered to be of high bioavailability; for the purpose of human health risk assessment, the substances molybdenum (metal), ferromolybdenum, molybdenum dioxide and molybdenum disulfide are considered to be of negligible bioavailability.

For the purposes of risk assessment, the potentially absorbable dose (the sum of the absorbed dose, skin and stratum corneum tape strips 6 to 20) may be used. This corresponds to 0.21% for the low exposure scenarios (ca 42 µg Mo/cm2) and 0.16% for the high exposure scenarios (ca 215 µg Mo/cm2). This value also accounts for part of the material associated with the stratum corneum and the test was conducted with a highly water soluble form of molybdenum in an aqueous solution. Thus, these values are considered to represent a conservative estimate.

Because there is unlikely to be any direct exposure to molybdenum as a result of HCAT usage, the above data is considered to be sufficient.