Reproductive Toxins and Highly Toxic Chemicals
Carcinogens are defined as reproductive toxins and substances that possess high acute toxicity as particularly hazardous substances (PHS). Lab users handling and working with carcinogens need to take additional precautions besides handling toxic substances. Note that carcinogenic chemicals are highly toxic, therefore strong attention is required to be paid while working with these chemicals, particularly if the threshold limits for human health has not been determined. Carcinogens vary in dose requirements to produce a tumour in laboratory animals. In addition, there’s a limited standard to compare the carcinogenic effect between human and animal. Yet, any chemical that has lead to a malignant tumour in laboratory animals must be regarded as potential hazard to human health and be handled accordingly. All lab users who are in contact with these type of chemicals should be aware of the risks in a full extent. These chemicals often do not have an acute effect but long term, and the threshold limits are usually uncertain. Seek safer alternatives if possible.
The World Health Organisations International Agency for Research on Cancer (WHO-IARC) has classified carcinogens into three groups as follows:
Category 1 Established human carcinogens. There is sufficient evidence to establish a causal relationship between human exposure to these agents and the development of tumours.
Category 2 Probable human carcinogens. Evidence, usually related to long-term animal studies, suggests that human exposure may result in the development of tumours.
Category 3 Substances suspected of having a carcinogenic potential in humans. In these cases there is limited evidence from animal and epidemiological studies to suggest a hazard.
Exposure to carcinogenic chemicals can result from the following:
- Carcinogens may be absorbed through respiratory system via inhalation of dust or vapor, or both.
- Carcinogens may be absorbed through skin contact with spills or splashes, or through contact with contaminated clothing, benches, apparatus and floors.
- Carcinogens may be absorbed by ingestion for contaminated food. Never pipet by mouth.
- Carcinogens may be absorbed through eye membranes upon contact with dust, vapor or splashes.
There must be a designated area in the laboratory to work with carcinogenic materials. Hands must be thoroughly washed before and after use. In these designated area, several additional precautions need to be taken:
- Always work under a fume hood. The airflow of this fume hood must be at least 0.60 m/s. The exhaust of fume hood should not be fed back into laboratory. Exhaust should also be discharged separately from others since it may create additional hazard risks.
- The surface of working bench for carcinogenic materials should be non-adsorbent so that any spill can be easily cleaned.
Always wear full protective clothing including;
- Rubber, P.V.C. or polythene disposable gloves.
- Buttoned laboratory coats or preferably wrap around gowns, which tie at the back.
- Laboratory safety glasses, or a full-face safety shield if the possibility of a splash exists.
- An approved respirator with a suitable particulate vapour cartridge.
In case of an eye or skin contact with a carcinogenic chemical, the affected body part should be immediately washed with cold water for 15 minutes, at least. Hot water accelerates absorption, and water vapor may cause chemical particle to be inhaled through respiratory system. Washing should be continued until all the visible evidence of the chemical has been removed. Safety shower should be used if the area of containment is large, and all the clothing needs to be changed and washed separately from other laboratory apparatus.
Carcinogenic materials should be appropriately labelled and stored in closed screw cap containers. They should be separated from other chemicals. A logbook to record their use is strongly advised.
Destruction and Disposal of Carcinogenic Waste
A solution of sodium dichromate in strong sulphuric acid (i.e. chromic acid solution) destroys organic compounds. It takes one or two days to clean all residual organic compounds from materials if the solution is freshly prepared. Residual chromic acid can be disposed of via drain by flushing large amount of water.
A solution of potassium permanganate in acetone is added to carcinogens that readily oxidize to deactivate them. As an alternative, concentrated or 50% aqueous sodium hypochlorite can be used.
Nucleophiles such as water, hydroxyl ions, ammonia, thiols and thiosulphate deactivate alkylating, arylating or acylating agents can be destroyed. This nuclepohillic substitution reaction is easier if it takes place in ethanol.
Aflotoxins should be dissolved in acetone and added to a hypochlorite solution to destroy any 2,3-dichloroaflotoxin B1, which may have been formed.
A solution of potassium hydroxide in methanol deactivates Cyclophosphamide.
Polycyclic aromatic hydrocarbons can be easily oxidized in sodium dichromate-sulphuric acid mixture.