EPA Case # 5034 Docket Number: EPA-HQ-OPP-2011-006 7

THPS (CAS: 55566-30-8)

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6 M AY 2011 

## Tetrakis (hydroxymethyl) phosphonium sulfate

THPS

Chemistry Document

Steve Groome Global Regulatory Affairs & Product Stewardship Man ager May 2011

Contents

1. Introduction

2. Chemistry

2.1. What is THPS?

2.2. What are the degradation products of THPS?

2.3. How much formaldehyde can be produced?

3. Should THPS be regarded as a formaldehyde releas er?

4. ConclusionsEPA Case # 5034 Docket Number: EPA-HQ-OPP-2011-006 7

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6 M AY 2011 1. Introduction

Albright & Wilson (a company later acquired by Rhod ia) first registered THPS in the United States

in 1995.

The Agency published a docket in relation to THPS a ccording to the requirements of the review program detailed in Section 3(g) of FIFRA.

Summary document (Docket Number: EPA-HQ-OPP-2011-00 67) explains that "The Agency believes that THPS may be a formaldehyde releaser b ecause it contains a hydroxymethyl group, which is essential to the production of formaldehyd e".

Rhodia and the Agency held an informal conference c all on 27 January 2011 to discuss this matter. Rhodia agreed to compile an explanatory ‘ch emistry document’ for the Agency. That is the purpose of this document.

2. Chemistry

2.1 What is THPS?

The active substance, Tolcide® PS75, is a 75% solut ion of THPS in water.

2.2 What are the degradation products of THPS?

The manufacturing concentrate and all end use produ cts are stable. The formaldehyde concentration in the commercial product is low and is closely controlled. The product of course conforms to OSHA requirements (29CFR1910.1048 for h azard communication).

THPS is always used in water. The degradation in wa ter has been followed analytically on many occasions and the following reaction scheme shows t he main steps: 

# T etrakis H ydroxymethyl P hosphonium S ulfate ( THPS )



# HOCH 2 

# C P + 

# CH 2 

# OH SO 4 2

-



# CH 2 

# OH

CH 2 

# OH

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6 M AY 2011 THPS THPO Formaldehyde Sulfuric acid

When THPS concentrate is diluted in water to ppm le vels, as it is used as a biocide, it will begin to hydrolyse in the presence of even the smallest conc entrations of dissolved oxygen. The initial degradation follows the reaction shown above.

THPS degrades to form THPO plus small amounts of fo rmaldehyde and sulfuric acid, all of which are very soluble in water.

THPO is tris (hydroxymethyl) phosphine oxide, which is a less reactive compound than THPS. The phosphorus in THPO is in a more stable oxidation st ate. However THPO is not a biocide and it was found not to have adverse effects on aquatic or ganisms tested (invertebrates, benthic organisms, fish and algae from freshwater and seawa ter).

In addition, in biodegradation studies, or followin g prolonged hydrolysis, further breakdown can occur, resulting in complete mineralization to carb on dioxide, water and inorganic phosphate. Rhodia is in possession of studies using radiolabel led THPS which show ready biodegradation to give 14 CO 2 . Therefore, as THPO is the major first degradate o f THPS, it may also be concluded that THPO is not persistent in the environment.

2.3 How much formaldehyde can be produced?

When THPS is used as a biocide, analysis confirms T HPO as the main degradant. When THPS reacts to form THPO the stoichiometry is as follows :

1 mole THPS → 2 moles THPO + 2 moles formaldehyde + 1 moles sulf uric acid

406 g THPS → 60 g formaldehyde

If the dose level of THPS is 10 ppm, it will produc e only 1.5 ppm of formaldehyde in solution. As we will see in section 3 of this report, this level is insufficient to be efficacious in most circumstances. The formaldehyde is produced in wate r and formaldehyde is readily biodegradable. Due to the use pattern of THPS, inha lation of treated water is not foreseeable. Dermal exposure to a solution of formaldehyde (at t he ppm level) should not give rise to concern.
For an industrial biocide, short duration and infre quent dermal exposure should be the worst case

encountered.

In the most severe hypothetical case that THPS was to be completely mineralized to carbon dioxide, water and phosphate, the degradation would be expected to occur via the production of formaldehyde, which itself is rapidly degradable – but only in water and over an extended period of time (the normal duration of a ready biodegradabili ty is 28 days). In this worst case, 1 mole of THPS would produce 8 moles of formaldehyde. This me ans 406 g of THPS would produce 240 g formaldehyde, and 10 ppm THPS would produce 5.9 ppm formaldehyde in water. It should be emphasised that the relative rates of formaldehyde production and removal make it extremely unlikely that this concentration of formaldehyde wo uld ever be present in any practical situation. HOH 2 C P + CH 2 OH SO 4 2

- 2 HOCH 2 P CH 2 OH + 2HCHO + H 2 SO 4 2

-

2 CH 2 OH

O CH 2 OH CH 2 OH

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6 M AY 2011 Rhodia has data on the rates of hydrolysis in aerob ic and anaerobic conditions; the rates of removal of formaldehyde from aqueous solutions (by hydrolysis, biodegradation, etc) are well

known.

Formaldehyde is very soluble in water. The correspo nding concentration in the headspace can be calculated to be very low compared to the concentra tion in solution.

3. Should THPS be regarded as a formaldehyde releas er?

Formaldehyde release agents (FRAs) release formalde hyde and their efficacy is comparable to that of formaldehyde. Their purpose is to produce f ormaldehyde in-situ to avoid handling of formaldehyde, or to provide slow delivery of formal dehyde. This definition is widely held within the industry, and within companies servicing water trea tment applications. FRAs are a category of insitu biocide.

The THPS molecule is the biocidally active agent. T he effectiveness of THPS is not dependent upon release of formaldehyde. In fact, THPS is more effective than formaldehyde; it is faster acting than formaldehyde, and it is effective again st ‘formaldehyde-resistant’ bacteria.

THPS has different modes of action to formaldehyde. Formaldehyde is deactivated by hydrogen sulphide, whereas THPS is not. In oilfield applicat ions, THPS is effective in sour systems whereas formaldehyde is not.

The biocidal mode of action of formaldehyde is well documented. It works by protein denaturing (cross-linking) of proteins in cell structures (Ref erence: Hugo (1971), Inhibition and Destruction of the Microbial Cell). In contrast a 1986 Albright & Wilson study identified multiple modes of action for THPS against sulfate-reducing bacteria: protein denaturing, enzyme destruction and inhibition, interference with the ADP-ATP energy cycle, and inh ibition of sulfate reduction.

Although THPS degradation results in the production in solution of small amounts of formaldehyde, its biocidal mechanism is not depende nt upon the released formaldehyde. In fact, the THPS molecule is the active agent and the prese nce of the THPS molecule results in quicker and more complete protein denaturing, and in format ion of stronger, irreversible protein crosslinks.

The cross-linking mechanisms are different for THPS and formaldehyde:

THPS mechanism: P-CH2OH + H2N-R  ...P-CH2NH-R

Formaldehyde mechanism: HCHO + H2N-R  ...CH2-NH-R

The presence of the P-C-N bond is critical: such bo nds are very stable and result in irreversible cross-linking which results in greater biocidal eff icacy.

Because THPS is not a FRA, its use patents are very different to that of FRAs and reflect different
use patterns.

For all these reasons, THPS should not be considere d a formaldehyde releasing agent.EPA Case # 5034 Docket Number: EPA-HQ-OPP-2011-006 7

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6 M AY 2011 4. Conclusions

In use, the degradation of THPS does result in the production of small quantities of formaldehyde. However, these levels do not present a risk to huma n health or to the environment. The concentrations that are produced are unlikely to be effective as a biocide.

The THPS molecule is biocidally active. The mode of action of THPS is not dependent upon released formaldehyde. THPS is more effective and faster acting than formaldehyde. THPS is effective against ‘formaldehyde resistant’ bacteria

.

There are many reasons why THPS itself must be cons idered as the sole active biocide.

THPS is not a formaldehyde releasing agent, as defi ned and accepted by the biocides industry.