Going Beyond Hazardous RISKS in Speciality Chemicals

By June 29, 2022 No Comments

Speciality Chemicals hazardous RISKS

This month saw policy makers and experts come together to discuss revision in REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) as part of the European Chemical Strategy for Sustainability which aims to achieve the zero pollution by 2050

The ecotoxicologist for the Belgium SME Altertox, Leonie Mueller said and I quote, ” If we want to protect human and the environment, we need to understand the way in which chemicals cause harm”

According to a recent report by the Lancet Commission on Health and Pollution, chemical pollution caused 1.8 million deaths worldwide, which include 900,000 deaths from lead pollution, which is more than from HIV/Aids. Lead poisoning could significantly reduce intelligence across large populations.

The number of deaths from chemical pollutants was likely to be an underestimate, the scientists said, as only a small proportion of the 350,000 synthetic chemicals in use had been adequately tested for safety. The cocktail of chemical pollution that pervades the planet has passed the safe limit for the stability of global ecosystems upon which humanity depends, researchers reported in January. 

Despite this alarming figure, experts believe – as long as we improve our knowledge and regulation of chemical hazards and reduce risks from exposure. However, without sufficient data, neither harmful chemicals nor safety exposure thresholds can adequately be identified in a timely manner.

To ensure we live in a safer world our principals Robinson Brothers, manufacturers of Speciality chemicals constantly research to manufacture safe chemicals. Based out of the UK, Robinson Brothers along with Nike, the popular sports shoe maker, reviewed via an independent consultancy the toxicological properties of two rubber accelerators for use in the manufacture and use of shoe components. The two accelerators are as follows

MBTS – Mercaptobenzothiazole disulfide

AS100 – Diisopropylxanthogen polysulfide


The data suggests that the exposure to AS100 in the finished article will be greatly reduced compared to MBTS. This will logically lead to minimal risk to health on exposure.  What is assumed is that the fundamental relationship that Risk is equivalent to Exposure multiplied by Hazard.  Robinson Brothers state that their Risk Consideration is based as follows

Risk = Exposure X Hazard

Both Toxicological properties and Exposure data of the individual accelerator and any breakdown products remaining in the vulcanised article are required to complement a Risk assessment. To ensure healthy and safe environments, assessing risk is a process by which hazards and reduced and eliminates risks.

Let us consider that

  1. If Exposure were zero, Risk could be considered to be zero.
  2. Similarly reducing Exposure whilst Hazard is constant, Risk will be proportionately reduced. It is a given that the Hazard of the accelerator cannot be changed. It is inherent to the molecule.
  3. Exposure can be varied which will increase or decrease the Risk.

The following covers both a quantitative Exposure analysis of the two target molecules by migration and total solvent extraction. The Toxicology data is taken from data held by Robinson Brothers and the public domain.

Comparison of Exposure and Toxicology data is made and conclusions drawn on the Risk of use of the candidate molecules.

Exposure Data

In all cases, synthetic polyisoprene was vulcanised with the corresponding accelerator at 0.75phr. 

Other ingredients include 

Active zinc oxide 0.6phr, stearic acid 0.6phr and sulphur 1.2phr.

The compound was vulcanised at 150 °C. Cure time was determined dependent upon the t90. 2mm thick films were produced by compression moulding. 

From each plaque 5 by 1” squared samples were cut and placed in 200ml of migratory solvent, separated by glass beads. 

Extraction was carried out for 24hours at 40 °C. The amount of accelerator which had migrated/been extracted was determined.

Solvents used were distilled water, 10% ethanol, 3% acetic acid and hexane (total extraction).

AS100 was determined by High Performance Liquid Chromatography, a technique for separation. Detection limit 0.1 ppm.

MBTS was determined by UV spectroscopy

Standard calibration curves were established before use

AS100 extraction study was carried out by RAPRA (independent consultants): Report number. 46121(13-04-2006)

Nature of solvent Condition of extraction Concentration extracted (g/100g or rubber)
Distilled water 40°C/24hours 0.0750 0.0004
10% ethanol 40°C/24hours 0.0860 0.0001
3% acetic acid 40°C/24hours 0.1980 <LOD
  • Hexane extraction not quoted as other components from the vulcanised rubber were extracted and interfered with UV absorptions of MBTS.
  • In the case of AS100, 99.83% was utilised on vulcanisation. Therefore 0.17% of AS100 per 100g of rubber is the maximum that could remain as residue.

In addition
Robinson Brothers commissioned a fume study with RAPRA (project no. AL0.159 of 24-06-2004). The fumes evolved during vulcanisation were captured using static and dynamic headspace. The fumes were separated by Gas Chromatography (an analytical technique used to separate chemical components of a sample mixture) and individual peak were analysed by mass spectrometry.


Volatiles evolved during vulcanisation

Volatile species Concentration (ng/g)
Carbon disulfide ~10,000
Isopropanol ~80,000
Di isopropyl dithiocarbonate 70-90



  • Isopropanol and carbon disulfide are essentially the main break-down products of AS100 on vulcanisation. Both being gaseous are volatised out of the polymer film. The diisopropyldithiocarbonate found in ppb quantities is probably responsible for the characteristic odour found when vulcanising with AS100. However, this species is unstable and decomposes to isopropanol and CS2. Extraction data indicates that AS100 has been totally consumed on vulcanisation with minimal exposure in the finished article.


  • Extractable residues from the MBTS cured samples have been shown to be 100 times greater than found with AS100.



LD50, oral, rat = 1500mg/kg LD50, dermal, rat = 2000mg/kg Skin sensitizer

Not classified as skin irritant (based on test results)

NOEL 12mg/kg/day (28 day oral study) No evidence of mutagenicity/clastogenicity


LC50, fish = 0.27mg/l EC50 daphnia = 0.15mg/l

EC50 algal inhibition = 0.10mg/l

Not readily biodegradable (10-15% after 28 days)

Main hydrolysis products confirmed as di- isopropyl xanthogen disulfide and sulfur


LD50, oral, rat >7940mg/kg LD50 dermal, rabbit >7940mg/mg Skin sensitizer

Not classified as skin irritant


LC50, fish = 82mg/l EC50 daphnia = 82mg/l

EC50 algal inhibition = 0.7mg/l Not readily biodegradable

  1. Data held by Robinson Brothers and included on the safety data sheet for Robac AS100.
  2. Data included on Flexsys data sheet for MBTS

Comparison of Toxicology

  • Environmentally toxicity is very similar to both candidate molecules having R50 and R53 labelling requirements
  • Both molecules are inherent skin sensitizers
  • Neither is classified as skin irritant
  • Neither is classified as mutagenic


Based on: Risk = Exposure X Hazard the following conclusions may be drawn

  • Toxicology results show both of the candidate molecules could be potential skin sensitizers if present as residue on the surface of the finished article. The level of exposure governs the magnitude of Risk as the Hazard is equivalent for both molecules.
  • As AS100 is totally consumed on vulcanisation leaving negligible residue the exposure will be proportionately reduced (factor of 100 compared to MBTS) considerably reducing the Risk.
  • MBTS has similar toxicological profile to AS100 but the exposure data shows a potential to leave 100times more residual accelerator in the finished article compared to AS100.

In Summary
The silent threat of chemical pollution is real and ubiquitous.  Chemical manufacturing is increasing at a rate of about 3·5% per year and is on track to double by 2030. Three particularly worrisome, and inadequately charted, consequences of chemical pollution are developmental neurotoxicity, reproductive toxicity, and immunotoxicity.

Over 200 chemicals, including lead, methylmercury, polychlorinated biphenyls, arsenic, organochlorine and organophosphate pesticides, organic solvents, and brominated flame retardants are neurotoxic to humans and especially so in younger children during developmental stage of life, from fetal to postnatal life-stage.

Evidence is strong and growing that exposure to particular manufactured chemicals, even at low doses, can have adverse effects on fertility and pregnancy. Pesticides, industrial chemicals (eg, halogenated flame-retardants, plasticisers, and dioxins), environmental chemicals of pharmaceutical origin, and toxic metals have been linked to a range of reproductive problems. Prenatal and early postnatal exposure to chemicals also appear to be linked to an increased incidence of reproductive diseases later in life, including endometriosis, breast cancer, cervical cancer, uterine cancer, and testicular cancer.

Some pollutants are toxic to the immune system. For example, perfluoroalkyl acids have been associated with reduced antibody responses to vaccines, increased risk in children for hospitalisation with infectious disease, and increased severity of COVID-19 infections. Many other chemical exposures have been shown to be toxic to the immune system in laboratory studies although research on the clinical consequences of exposure is still scarce.

 Economic impacts of pollution
The economic losses associated with deaths due to pollution can be valued by the output lost when a person dies prematurely (i.e., the human capital approach), or by using the value per statistical life (i.e., what people would pay for small risk reductions that sum up to one statistical life), which we refer to as welfare losses. The 2017 Lancet Commission on pollution and health, which used the value per statistical life approach, found that welfare economic losses associated with 2015 pollution were equal to 6·2% of world GDP, and 82% of these economic losses were attributed to ambient air pollution and household air pollution. GDP.

For most of the thousands of manufactured chemicals now in commerce there are no reliable data on developmental toxicity, reproductive toxicity, immunotoxicity, the effects of long-term low-level exposures, or the health risks of chemical mixture. 

Despite substantial progress in the international arena since the 1990s to establish multilateral agreements regulating some chemicals in waste, “the global goal of sound chemicals and waste management in ways that lead to minimized adverse effects on human health and the environment” has not been achieved.

I R Tubes Private Ltd., Pune are distributors for quality chemicals of Deutsche Oelfabrik of Germany, Omya UK Ltd., Robinson Brothers, UK, Emery Oleochemicals Ltd and Aquaspersions. Our chemicals are used in the manufacture of Rubber, Plastics, Latex, Adhesives and Sealants.

Raju Jethmalani

IRTubes Pvt. Ltd., Pune

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