In solid form, both of these chemicals carry significant hazards. Usually in schools, they are used as solutions. In considering safety aspects of any substance, it is important to consider both what is being used and how it is being used. Hazardous chemicals may be safe to use at concentrations which are below certain levels and/or where relevant control measures are implemented.
Phenolphthalein: Information from Safe Work Australia’s Hazardous Substances Information System (HSIS) provides the cut-off concentrations for hazard classification. The cut-off concentration is the concentration above which the hazard classification for the chemical applies. In the HSIS, Phenolphthalein has a cut-off concentration of 1%.
In schools, phenolphthalein is usually used at concentrations of 0.2%–0.5% in a 60% solution of ethanol. This is below the cut-off level for hazards for the phenolphthalein component. However, this solution still carries hazards due to the ethanol component. If you compare the Safety Data Sheet (SDS) of solid phenolphthalein alongside the SDSs of the 1% and 0.5% solutions you can see that at below 1%, the hazards refer to the flammable properties due to the ethanol.
Lead nitrate: Information from Safe Work Australia’s Hazardous Substances Information System (HSIS) provides the cut-off concentrations for hazard classification. Lead nitrate is not specifically listed and is considered, along with other lead compounds which have a cut-off concentration, safe at 0.5% lead ions in solution, see Lead compounds. Schedule 6 in the Work Health and Safety Regulations gives a cut-off value of 0.3% lead for Reproductive Toxicity category 1, one of the categories in which lead compounds are classified.
In schools, most solutions are made up in molar concentrations and so need to be converted to a percentage to compare with the cut-off values. Solutions of lead nitrate of concentration 1 M and 0.1 M would equate to 21% and 2.1% lead respectively, which are both above the cut-off value of 0.3%.
A 0.01 M solution of lead nitrate would have a concentration of lead ions below this cut-off value. Preparation of any solutions could potentially cause exposure to the solid chemical, but safe handling procedures will minimise this risk.
Risk Assessments: It is important to conduct a risk assessment taking into consideration the intrinsic hazards of a chemical. However, the use of controls such as safe handling procedures reduce the risk further by minimising exposure.
Safe procedures for handling solutions would include using small quantities for short amounts of time, wearing appropriate PPE such as gloves and safety glasses as well as good laboratory hygiene such as cleaning up any spills, no eating or drinking in laboratories and washing hands at the end of all laboratory sessions. When making up solutions from the solid chemicals, the additional control of conducting this in an operating fume cupboard should be used. Schools may prefer to purchase chemicals in solution form, rather than prepare the solution on-site.
We suggest that pregnant or breastfeeding women who are concerned about preparing a solution of a lead salt, discuss this with their employer and ask another trained person to prepare the solution.
In the past, there has been significant environmental exposure to lead through lead and lead compounds in the air through lead emissions from fuels. In addition, it was used widely in paints. The regulations, which have resulted in the removal of lead from paints and fuels, has greatly reduced the environmental exposure to lead. People working in occupations dealing with lead products on a regular basis, such as with lead batteries, smelters etc., are at a much higher risk of lead exposure.
In a school science setting, the use of lead and lead compounds is minimised through the use of small quantities, used for small amounts of time. However, precautions still need to be taken.
The following are some of the ways that lead can enter a body.
- Inhalation: It is possible to inhale lead through breathing in dust or chemicals that contain lead. If handling of the solid lead compounds is conducted in a fume cupboard, this reduces the risk of inhalation.
- Ingestion: It is possible to accidentally eat lead that may be on your hands when you eat or drink or engage in other activities that may transmit the lead to your mouth such as applying lip balm or smoking. If good laboratory hygiene, such as no eating or drinking in laboratories and washing hands at the end of all laboratory sessions is observed, then this reduces the risk of ingestion.
- Skin absorption: It is possible to absorb lead through the skin, but this would only be a small portion of lead if it is not washed off. If gloves are worn, and if hands are washed at the end of all laboratory sessions, then these measures reduce the risk of skin absorption.
Agency for Toxic Substances and Disease Registry, U.S. Department of Health and Human Services. 2007. Toxicological profile for lead, Agency for Toxic Substances and Disease Registry website, https://www.atsdr.cdc.gov/toxprofiles/tp13.pdf (August 2007)
‘Information on hazardous substances’ WA Department of Commerce website, https://www.commerce.wa.gov.au/worksafe/hazardous-substances-faqs (13 July 2016).
‘Lead compounds with the exception of those specified elsewhere in HSIS’ Hazardous Substances Information System (HSIS), SafeWork Australia website, http://hsis.safeworkaustralia.gov.au/HazardousSubstance/Details?hazardou...(Last accessed 15 July 2016)
‘Lead nitrate’, Safety Data Sheet. Chem-supply website, https://www.chemsupply.com.au/documents/LA0191CH3R.pdf (August 2015)
‘Phenolphthalein’, Hazardous Substances Information System (HSIS), SafeWork Australia website, http://hsis.safeworkaustralia.gov.au/HazardousSubstance/Details?hazardousSubstanceID=6456 (Accessed 23 May 2016)
‘Model Work Health and Safety Regulations’, Safe Work Australia website, http://www.safeworkaustralia.gov.au/sites/swa/about/publications/pages/model-whs-regulations (November 2011)
 ‘How can a chemical be considered safe when it is classified as a hazardous substance?’ From an archived version of the Department of Health National Industrial Chemicals Notification and Assessment Scheme (NICNAS) website, (Archived link created November 2016)
 ‘Phenolphthalein’ Safety Data Sheet. Chem-Supply website, https://www.chemsupply.com.au/documents/PA0331CH52.pdf (August 2011)
 ‘Phenolphthalein, solution 1% in ethanol’ Safety Data Sheet. Chem-Supply website, https://www.chemsupply.com.au/documents/FE0496_AU.pdf (July 2013)
 ‘Phenolphthalein, solution 0.5% in ethanol’ Safety Data Sheet. Chem-Supply website, https://www.chemsupply.com.au/documents/PL1011CH7R.pdf (August 2011)