You might be a bit confused by the title, but if not, that’s great. Otherwise, let me first explain a little bit about ecotoxicology and why it is also important from a cosmetic point of view. Ecotoxicology is a multidisciplinary field of study that focuses on understanding the impact of various chemical substances, contaminants, and pollutants on ecosystems, including terrestrial, aquatic, and atmospheric environments. It examines how these substances can be harmful to living organisms and the overall ecological balance.
And what is Zinc pyrithione?
Zinc pyrithione (ZnPT) is a coordination complex of zinc, synthetic chemical with fungistatic (inhibiting the division of fungal cells) and bacteriostatic (inhibiting bacterial cell division) properties. With a history of over 60 years in the cosmetic industry it has been a popular, widely used anti-dandruff ingredient used in hair shampoos, regulating sebum production, antibacterial and anti-itching .
Zinc pyrithione was included in the EU cosmetic ingredients ban as of October 2021. Starting from March 2022, cosmetic products are no longer allowed to contain this ingredient in the European Union. The decision to ban this ingredient is due to its potential ability to damage DNA. Namely, zinc pyrithione has been classified as a CMR substance of category 1B .
What does that exactly mean? EU cosmetics legislation contains provisions on the use of substances classified as carcinogenic, mutagenic, or toxic for reproduction (CMR substances) in cosmetic products. In general, the use of CMR substances is prohibited, apart from in exceptional cases .
CMR 1B category, in which zinc pyrithione is placed, stands for chemical substances for which there is scientific evidence based on animals that the substance is carcinogenic, mutagenic or reprotoxic … simply, this means, it can negatively influence reproduction potential, causes DNA damage and/or lead to cancer disease in animals.
On the Faculty of Environmental Protection, we decided to test this molecule in our lab using two commonly used ecotoxicological tests:
- Simple plant-based test using the oldest cultivated plant – onion (Allium cepa L. in Latin), which is used for the early evaluation of toxicity and genotoxicity of various molecules;
- And a small planktonic crustacean Daphnia (Daphia magna in Latin) which is a well-established and widely used model organism for freshwater toxicity testing as they are well characterised, have a rapid parthenogenetic reproductive cycle and show sensitivity to a range of environmental xenobiotics.
How did the experiment go and what did we find out?
Onions were exposed to different ZnPT solutions for 7 days, when the length of the roots were measured (Figure 2) and cell division was investigated under the microscope. On the other hand, Daphnia were cultivated in ZnPT solution for 24 and 48 hours in a chamber and afterwards the mortality was determined.
Results confirmed the toxic potential of zinc pyrithione, since the cell division and consequently roots growth was slowed down compared to the control plants. In the highest concentrations onions even stop to divide (Figure, on the right). In the Daphnia test, the mortality of the first three highest concentrations was 100 % already after 24 hours. When the ZnPT concentration was decreased, the mortality also gradually declined slowly.
Our results confirm that ZnPT is toxic to exposed organisms. In a way, we have confirmed that the molecule is not the safest one to use. Therefore, we are happy that this molecule is no longer found in the hair care products… unless you buy the product outside the EU, in certain regions, where ZnPT is not banned and is still present, usually in limited concentrations.
With this short experimental study and article, we would like to emphasize, it is important to understand each product we are using daily and know what kind of ingredients contains and in what amounts.
GS tip: Being more aware of the substances we use on our bodies and choosing a better and healthier option can help not only you but also protect our environment. For instance, when substances like the one we tested, come into contact with the environment especially in higher amounts, such as sunscreen or creams washed into lakes, rivers, and the sea while we swim, or while camping, where some wash themselves with shampoos in the river and not knowing the harm they can do. That is why it is important to be aware and informed, not letting the marketing deceive you with greenwashing, making it better for you and the environment.