Volatile Organic Compound Mixtures

Some mixtures of the vapours of volatile organic compounds contain substances which exhibit independent effects because they act on different parts of the body or by differing mechanisms, however it probably more common for components of a mixture to exhibit additive or synergistic effects.

When a person is exposed to two or more contaminants an additive effect occurs when the contaminants act on the same target organ or by the same mechanism. In such a situation the total effect on the body equals the sum of each of the individual substances. For substances whose effects are purely additive, conformance to the airborne exposure standard occurs when

Where C1, C2, …. Cn are the average measured airborne concentrations of the particular substances 1, 2, …n and L1, L2, ….Ln are the exposure standards for the individual substances.

When assessing the hazard from a mixture of airborne contaminants, it is important to identify and quantify all components in the airborne mixture as a number of factors such as particle size distribution or solvent vapour pressure give rise to substantial variations between the concentration of each component of the parent mixture and that which occurs in air.

If for some reason this cannot be done, then an alternative is to assume the mixture follows Raoult’s Law, although this law only applies to Ideal Mixtures. If Raoult’s Law is applied the theoretical composition of the vapour generated by a mixture can be calculated, however this method is less satisfactory as there is no truly Ideal Mixture although some mixtures go close. An Ideal Mixture may be described as a mixture of two liquids where there is zero enthalpy change in mixing, that is, the temperature doesn’t rise or fall when the two are mixed.

While exposure to some vapours is additive, eg through their general effect on the central nervous system via narcotic and anaesthetic effects, other solvents have deleterious effects on other organs and the assessment of a mixture must take account of the basis for any potential interactions.

There are some materials for which the deleterious effect of a mixture is multiplicative, synergistic or potentiative, not additive.

It should be clear from the above that a Consultant with expertise in assessing exposure to Volatile Organic Compounds, VOCs, is needed. A person with Chemistry, toxicology, thermodynamics, experience, and knowledge in various other technical fi elds is the preferred choice. All GETEX Consultants are Degree qualifi ed in a relevant Professional field. Senior staff have long experience in the industry.

GETEX holds Professional Indemnity Insurance and is NATA accredited to ISO / IEC17025 for chemical testing (certain tests only).

Before you choose a Consultant ask questions, check it out.

Download the Volatile Organic Compounds Mixtures Information Sheet (PDF)

Pesticides and Toxicity

Pesticides is the name given to a range of materials that kill or destroy unwanted forms of life. The pesticide is named according to what form of life is destroyed. For example, if unwanted plants, also called weeds, are destroyed the pesticide is called a weedicide or a herbicide. Hence the pesticide types are called miticides, insecticides, fungicides etc. A pesticide belonging to one group may also be effective in killing other unwanted pests, and so belong to two or more groups.

For centuries there has been a range of pesticides available, with a number of these still used today, including arsenic which is effective against a wide range of unwanted plants, insects, termites and bacteria; and copper sulphate used particularly to stop mildew on grape vines. These centuries old pesticides are mostly compounds of naturally occurring metallic elements such as arsenic, lead, mercury, copper, thallium. We learnt from the alchemists of old and their attempts to transmute base metal into gold that elements cannot be transmuted. Hence once applied they continue to exist where they were applied unless they are leached away by solution into water or oil if present, or physically transported away by being adsorbed to soil particles which are then physically washed away downslope or into a watercourse. They present a problem when, because of over application, their concentration becomes too high, for example excess copper in groundwater is a current problem.

Organochlorines are not highly toxic to humans but the difficulty is that they do not degrade quickly and they accumulate in fat so that predatory animals at the top of the food chain can end up with high concentrations in their bodies and these can have effects such as thinning egg shells. Because of this organochlorines were phased out and the more toxic organophosphates were introduced. These have the advantage of not lasting long in the environment. While they present an occupational toxicity problem for people applying them, their long term environmental effects are much reduced.

Herbicides cover a wide range of materials, depending on the type of herbage to be killed and whether some persistence when applied is desired or not. Some are quite toxic to people. One of Getex’s staff remembers being approached for help with an analysis method many years ago by people doing a post mortem on two people who had put a red wine coloured paraquat herbicide in a wine bottle for storage, then after a few drinks, had drunk the herbicide. This illustrates the importance of not storing anything other than food in a food container. Staff have also had more recent experience with again a paraquat herbicide applied in a significant quantity of water to the ground and running into the next property where racehorses were kept. One horse died with the herbicide being strongly implicated in the horse’s death.

It is interesting to note that the toxicity of a material to various animals depends on a number of factors. In the case of horses, the inability to regurgitate renders them more susceptible to toxins than bovines. As a general rule herbivores are more tolerant to toxins than carnivores as herbivores’ livers contain more enzymes to digest toxins which are usually of plant origin. Carnivores lack these enzymes, a good example being cats, which are difficult to treat with drugs or to sedate.

Contact GETEX for assistance with Pesticides

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Download the Pesticides and Toxicity Information Sheet (PDF)

Silicon, Silica, Silicates, Silicones

What is the difference? The mathematics of exposure

Silicon is a chemical element. It is the second most abundant element in the earth’s crust after oxygen. Compounds of silicon and other elements form a range of substances including silica, silanes, silicates, and silicones. Naturally, silicon usually occurs as silica.

Silica is a compound of silicon and oxygen known as silicon dioxide. It occurs in sand, quartz and opal. Silica can exist as crystalline and amorphous forms. The prolonged inhalation of fine crystalline silica dust, even at low concentrations, is associated with silicosis. Amorphous silica is much less pathogenic than crystalline forms. Silica dust is formed in many processes connected with the construction industry, such as cutting, drilling or grinding cement or sandstone. Long term inhalation of fine silica dust causes irritation to the lung tissue. Early symptoms include breathlessness during exercise. Over a period of 10 to 20 years silicosis develops. Once the disease has begun it will continue to progress even if the person is removed from further exposure. There is no known cure. People with silicosis are at greater risk of developing lung cancer.

Silicates are compounds of silicon, oxygen and metals. Silicates are found in granite, asbestos and feldspars. Long chain silicates are found in asbestos. Exposure to asbestos can have long term adverse heath effects, although not all silicates have such an adverse effect.

Silicones are synthetic polymers with a linear repeating silicon-oxygen backbone. Organic groups attached directly to the silicon atoms prevent formation of the three dimensional network found in silica. Certain organic groups can cross link two or more of these backbones, enabling a wide range of products to be manufactured, including silicone rubber, silicone gels and silicone oils. A common silicone polymer is polydimethylsiloxane

Monomeric silicon based chemical structures similar to carbon based structures are known as silanes. They are commonly used as chemical coupling agents.

The adverse health effects of silica and asbestos are multiplied by simultaneous exposure to other irritants such as tobacco smoke. It might be noted here that:

1. As a rule the risk associated with exposure to carcinogens is proportional to  the amount of material the person is exposed to, that is the Dose, D,    and the duration of exposure, d, to the fourth power. Hence a long exposure to small doses is much worse than a short term exposure to a big dose.
2. It can easily be assumed that everything must always add up to 100% but this is not the case. While the effect may be 100%, say death from lung cancer, the causes may add up to more than 100%. That is, any of the causes such as asbestos or smoking can produce the effect alone, but they can have an additive or multiplier effect when exposure is to all of them together.

 

Contact GETEX for assistance with Silicon, Silica, Silicates, and Silicones

GETEX operates 24/7. Your call will be handled by experienced people with authority who can help you. We do not use message services.

Download the Silicon, Silica, Silicates, and Silicones Information Sheet (PDF)