It’s all in the dose: Toxins, carcinogens and poisons

It’s all in the dose: Toxins, carcinogens and poisons

Toxicity assessment of any chemical (usually through animal studies) is quite a complex process and there are many factors that can affect the degree of toxicity. Some of these factors include:

  • The animal, its age, sex, initial health
  • The exposure route: Oral, dermal absorption, inhalation, and ingestion
  • Environmental conditions: temperature, vapour pressure, movement of air/water or soils
  • The dose response: Two comparable chemicals classed as toxic, yet one of them will start producing noticeable effects at lower doses.

Most of the base ingredients used in cleaning detergent formulation has at some point been tested on animals, this includes ingredients used in ‘ethical’ cleaning products.


From theses studies, an often quoted ‘toxicity value’ is calculated, this value is called the LD50 value, or Lethal Dose value. This value can be found on the MSDS (Material Safety Data Sheets) for the chemical, and many other risk assessment documents. The LD50 value, quoted in milligrams per kilogram of body weight, is the median lethal dose in pure form that is lethal to 50% of the test animals within the duration of the assessment. It is the most widely used and most misunderstood guide to the toxicity of a chemical.

By that definition, LD50 is effectively limited to measuring the acute toxicity and ignores any non-lethal response, like rashes, irritations and reactions like nausea. This is quite key point, because a chemical might have a very high LD50 (it requires a very large dose to be lethal on average) but produce local or systemic toxic effects at a much smaller dose, the threshold level, like severe skin irritation or severe nausea. Also, it is very important to understand the route of exposure when looking at the LD50 for a particular chemical; The LD50 for oral administered dose will be different compared to inhaled or adsorbed dose and comparing the LD50 for multiple routes, you can get some idea of the safety precautions that need to be put in place.

For example, you’ll see a chemical labelled with an LD50 Oral at 500mg/kg and LD50 dermal at 2000mg/kg. For an average 70Kg person, this translates to 35g as an average lethal dose orally and a 140g dose adsorbed through the skin. This might not sound a lot, but you have to remember that this is 35g and 140g of the pure chemical. If this chemical was an additive in some cleaning detergent, you are therefore very unlikely to come across it in pure form (with a few exceptions like organic solvents). In a typical cleaning detergent formulation, the concentrated form, that is prior to diluting with water, will contain a range of individual component chemical ingredients at around 1-20% by volume. Upon dilution, this concentration reduces even further to around 1/100th or 1% of the original concentrated form. As you can see, you are effectively only dealing with minute amounts of the chemical ingredient at any one time.

As I have already alluded to, a much more useful guide is to gain some understanding as to the sub-lethal toxic effects and at what dose those effects start to be noticed – the threshold level. On an MSDS sheet you will often see a range of LD50 values for a particular ingredient: it will indicate the animal, the route of exposure and the LD50 value. It is important to understand that the range of LD50 values will vary tremendously between the different routes of exposure. For example, if the chemical is given orally or injected (intravenous) then the LD50 value could be much lower than the chemical adsorbed into the skin (dermal). There are exceptions, but by comparing the values for the different routes of exposure you can get some idea as to the likely dangers. In conjunction with the physical use and the chemical properties of the chemical in question, the LD50 values can give you some insight into the sub-lethal effects and the likely PPE required to provide a sufficient barrier.


Take for example a liquid cleaning detergent, it doesn’t really matter which one, one that requires dilution and applying either by machine or by cloth and bucket. Mentally go through the various steps in handling the concentrated form, through to dispensing and diluting it, to using the product and removing the waste. At each one of these steps there is a risk of exposure to the chemical product and a there are a number of probable routes of exposure. For example, if you are simply pouring out a measured amount of the chemical product into some container, then you are likely to splash some on to your skin, face or even your eyes. Obviously in this example you would insist on adequate hand and face protection, or change your dispensing system to reduce the risk.

Another example is in the use of spray bottles or spray cans (pressurised and hand-operated), common in the hospitality industry. These devices create a very fine mist of macroscopic droplets dispersed into the environment, turning a low to no inhalation risk (liquid form) into a very high inhalation risk to the operator and to anyone in the immediate area. The risk of dermal absorption, including soft tissue absorption like eyes, gums and nasal passageways, also increases. The degree of risk depends on the toxicity in the relative LD50 values for inhalation and dermal absorption values, if provided.

In these two examples, the possible routes of exposure are obvious. By examining each step as mentioned above, you can determine the risk and put in place appropriate safety measures. This simple process will cut down virtually all the risk to the operator. You do need to take into account people with sensitive skin and provide appropriate safe measures for them.


Paracelsus (1493-1541) coined the adage “All substances are poisons; there is none which is not a poison. The right dose differentiates a poison…’, or more popularly known as ‘the dose makes the poison’. The threshold limit mentioned earlier marks a point when toxic effects start to make themselves apparent – only when the dose reaches a certain level, below which no ill effects are evident. Paracelsus said all substances and people often fail to appreciate that every substance, including water and oxygen, in sufficient amounts (dose) is toxic. If you were to drink approximate 6 litres of water in a relatively short time, you can suffer from hypoatremia (water intoxication) where the excess water reduces your normal sodium balance beyond the safe limits, this can be fatal and has been known to be the cause of death in some long distance runners. Conversely, a highly toxic chemical taken in low enough doses will produce no toxic effects at all. Botox is a good example; the neurotoxin in the treatment for muscular disorders and for cosmetic therapy is one of the world’s deadliest toxins, you would only need around 100ng or about 0.0000001 grams to kill an average person. Treatments with doses significantly below this lethal dose are an effective medicine, with only minor and temporary side effects.

It is interesting to note that the list of the world’s most deadliest toxin are naturally occurring, so because a cleaning chemical ingredient is synthetically manufactured does not automatically mean it’s dangerous or toxic.

Take the Chemical Proficiency Course (hosted on

section-6-part-2-smallThis course aims to provide the vital training in the safe use, handling and storage of cleaning chemicals. To do this, you will need to know how to read and interpret all sources of information given to you and be able to create a COSHH risk assessment. This course will take you through the old CHIP regulations and introduce to you the new CLP and REACH regulations (the latter two replaces the CHIP in 2015) and how these new regulations affect the decisions you will need to make when assessing risk.

Rafael Cobos