Toxicological Evaluation and Limit Values for Nonylphenol, Nonylphenol Ethoxylates, Tricresyl, Phosphates and Benzoic Acid

1. General description

1. General description
1.1 Identity
1.2 Physical/chemical properties
1.3 Production and use
1.4 Environmental occurrence
1.5 Environmental fate
1.6 Human exposure

Tricresyl phosphate exists as 10 different pure isomeric substances with the three cresyl groups being either ortho, meta, or para.

The name tricresyl phosphate is used as a common name for the ten substances and for mixtures of these. The relative content of the different cresyl moieties depends on the cresols used in the production of tricresyl phosphate. Industrial-grade tricresyl phosphate contains predominately the meta- and para-isomers and modern mixtures contain less than 1% of the ortho-isomer.

This document will deal with both the mixed tricresyl phosphates and with the pure tri-ortho, tri-meta, and tri-para-cresyl phosphates. In addition, studies, where tricresyl phosphate is the major constituent, are included, as long as they are sold / named tricresyl phosphate e.g. studies with mixtures where cresyl-xylenyl or cresyl-phenyl phosphates occurs.

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1.2 Physical / chemical properties

1.3 Production and use

The world production of TCP in unknown but Japan produced 33000 tonnes in 1984, USA 10400 tonnes in 1977, and China produced about 1000 tonnes in 1989 (EHC 1990).

TCP is produced by the reaction of cresols with phosphorous oxychloride. The cresols can be derived from cresylic acid or tar acid, which is a mixture of isomers of cresol and varying amounts of xylenols, phenol, and other high-boiling phenolic fractions obtained as a residue from coke ovens and petroleum refining. Using this source of cresol in the synthesis yields a very heterogeneous TCP. Another source of cresol is synthetic cresol, prepared from cymene via oxidation and catalytic degradation. This process can after purification yield ortho-, meta-, and para-cresol of high purity, which can be used to synthesise the pure tri-o-, tri-m-, and tri-p-cresyl phosphates. Mixing pure meta- and para-cresol together with phosphorous oxychloride can give TCP with variable isomer composition e.g. different proportions of the four possible combinations of meta- and para-cresyl phosphates. (EHC 1990).

TCP has many uses. It has been used since the start of the century in hydraulic oils. Other main uses are as a plastisiser in vinyl plastic manufacture, as a flame-retardant, a solvent for nitrocellulose, in cellulosic molding compositions, and as an additive to extreme pressure lubricants. Minor uses are in cutting oils, machine oils, transmission fluids, and cooling lubricants. Other minor uses are as an additive in making synthetic leather, shoes, polyvinyl acetate products, as solvent for acrylate lacquers and varnishes, and in non-smudge carbon paper. (Various authors quoted from EHC 1990).

1.4 Environmental occurrence

TCP does not occur naturally in the environment.

TCP is released to air, water, soil and sediment as a result of its production, processing and use. The majority of TCP release to the environment is accounted for by end-point use (particularly volatilisation from plastics and leaking hydraulic fluids) rather than production. (EHC 1990, HSDB 1998).

No data are available on the release of TCP to the atmosphere from production processes. However, open, high-temperature processes such as roll milling, calandering and extrusion of plasticised polymers may result in significant gaseous emissions of aryl phosphates including TCP (Boethling & Cooper 1985 - quoted from EHC 1990).

TCP levels of 0.01-2 ng/m³ in air collected at production sites in USA have been reported (MRI 1979 - quoted from EHC 1990). Near heavily industrialised cities in Japan TCP levels of 11.5-21.4 ng/m³ were found in three out of four samples, and in samples of urban air TCP levels of 26.7-70.3 ng/m³ were recorded in three out of 19 samples (Yasuda 1980 - quoted from EHC 1990).

TCP is slightly soluble in water. It has only occasionally been detected in water samples (several authors - quoted from EHC 1990). In 13 out of 84 Canadian drinking water samples, TCP was detected in concentrations of 0.3-4.3 ng/l (EHC 1990). The adsorption coefficient of TCP on marine sediment was found to be 420 (Kenmotsu et al. 1980 - quoted from EHC 1990).

TCP has been detected in soil at a chemical plant at a level of 1.0-4.0 mg/kg (Boethling & Cooper 1985- quoted from EHC 1990).

In a Danish study TCP was detected in sewage sludge at levels of 57 to 12,000 µg/kg dry matter in 11 of 20 representative sewage treatment plants. In water extracts from the same sewage treatment plants TCP was found in 9 plants with a mean concentration of 1.50 g µ/l (range 0.15 - 3.80 µg/l). (MST, 1996).

As TCP has a log P_{octanol/water} of 5.11, and as it is found in sewage sludge, bioaccumulation of the substances can occur. Bioconcentration factors of 165-2768 have been measured for several species in laboratory tests (EHC 1990). The levels of TCP given for fish and shellfish below are indicative of this, as up to 3.3 g µ/l is found in water extracts from Danish sewage treatment plants (MST 1996). This concentration will, when distributed over a greater water volume, fall considerably.

A concentration of 40 ng/g of TCP has been found in sturgeon from the Colombia River, USA (Lombardo & Ergy 1979 - quoted from EHC 1990). In fish caught near triaryl phosphate manufacturing plants 2-4 ng TCP/g were found (Muir 1984 - quoted from EHC 1990). In samples of fish and shellfish caught in the Seto Inland Sea, Japan, TCP levels of 1-19 ng/g was found in 4 out of 41 samples (Kenmotsu et al. 1981 - quoted from EHC 1990).

1.5 Environmental fate

Air

If released to the atmosphere, TCP will degrade in the vapour-phase by reaction with photochemically produced hydroxyl radicals with an estimated half-life of 26 hours). Physical removal of particulates from air by dry deposition (settling) and wet deposition (rainfall) can occur. (HSDB 1998).

Water

TCP released into water is readily adsorbed on to sediment particles, and little or none remains in solution (EHC 1990).

Biodegradation is an important process in aerobic waters. Screening studies suggest that TCP will be biodegraded at moderate to rapid rates with half-lives on the order of several days or less. Biodegradation under anaerobic conditions is unclear.

TCP can also degrade through aqueous hydrolysis. The neutral hydrolysis half-life at pH 7 and 25° C is about one month; the hydrolysis rate will increase as the water becomes increasingly alkaline. (HSDB 1998).

Among the isomers of TCP, the ortho isomer degraded in river water slightly faster than the meta isomer and both isomers degraded faster than the para isomer (Howard & Deo 1979 - quoted from EHC 1990).

Soil

Biodegradation is expected to be a dominant degradation process in soil. TCP is relatively immobile in soil as it adsorbs strongly to soil and is not expected to leach. (HSDB 1998).

Sediment

TCP is readily biodegraded in sewage sludge with a half-life of 7.5 hours, the degradation within 24 hours being up to 99% (EHC 1990).

Even though TCP’s are degraded within 5 days in sewage treatment plant sludge, the substances are often found as pollution’s in nature due to their very widespread use.

Biodegradation pathway

The degradation pathway for TCP most probably involves stepwise enzymatic hydrolysis to orthophosphate and phenolic moieties; the phenol would then be expected to undergo further degradation.

1.6 Human exposure

No data have been found.