Fundamental environmental and biological impacts of using calcium carbonate particles and calcite-based emulsions

Pierre Trinh | Sustainability researcher

Edited by Maria Fernanda Gonzalez Prato

14th March 2024

Keywords: calcite, stabilizers, emulsions, cytotoxicity, aquatic ecosystems

Previously, a former researcher at The Skynth Research, Tries Apriliando, analyzed how limestone explored in an Indonesian mine can cause massive damage to the nation’s environment, which is characterized by various natural features, from rocky ground and caves to underground rivers and surface streams. But this was only the tip of the iceberg. Not only can the mining of limestone possibly pose a huge threat to global biodiversity in the long term, but using this mineral as a cosmetic ingredient may also severely affect vulnerable consumers who utilize the product on a daily basis. In this article, our senior researcher, Pierre Trinh, will further discuss these problems and, if possible, render a more sustainable purchasing option to consumers and manufacturers.

What should we know about calcite ingredients?

According to Apriliando (2023), calcite, or calcium carbonate (CaCO3, or CC), is either a white, odorless powder or colorless crystal practically insoluble in water, which has been ubiquitous in rocky mountains globally. Round calcium carbonate (CAS: 1317-65-3) results directly from the mining of limestone (U.S. National Library of Medicine).

In 2023, an American market analysis demonstrated that the use of calcite crystals as a natural exfoliant and skin-brightening agent has been gaining widespread popularity, even as stabilizers for cosmetic Pickering emulsions, especially among the millennial population (Nationwide Research, 2017). It is anticipated to rise at a compound annual growth rate (CAGR) of 4.65 until 2035 (Mineral Technologies Inc., 2023).

Is the calcite ingredient really sustainable?

Let’s discuss the sustainable aspects of calcite carbonate (CC) particles applied as stabilizers for emulsion and CC-stabilized emulsion. In principle, it is logical to analyze these materials’ cytotoxicity, particle morphology, and size distribution in order to further understand their environmental and biological impacts. As the main medium through which the particles infiltrate and diffuse into other environments, aquatic ecosystems (i.e., rivers, lakes, and oceans, unnatural water bodies) should be well investigated with respect to the environmental behavior of the particles. Reportedly, an aquatic environment receives runoff and wastewater from domestic and industrial sources and is an important gathering place for various pollutants. (Sun et al., 2022)

To uncover the cytotoxicity of the particles, Marto et al. conducted a series of in-vitro assays over the spontaneously immortalized human keratinocyte cell line HaCaT (CLS, Eppelheim, Germany). Briefly, cells were incubated within 24 hours with both CC-stabilized emulsion (100 μg/mL) and CC particles (6.25 μg/mL), and then the cell viability was calculated using the endpoint MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide) reduction assay.?

Meanwhile, the morphology of CC particles was studied using a scanning electron microscope (SEM) Phenom ProX, produced by Thermo Fisher Scientific (FEI) in Eindhoven, The Netherlands. Micrographs were acquired using a backscattered electron detector (BSED) with a beam acceleration voltage of 10 and 15 kV at 1.0 Pa, with an optional sample treatment. The particle size distribution was determined using a Malvern Mastersizer 2000 (Malvern Instruments, from the UK) coupled with a Hydro-S accessory with a default refractive index (RI) of 1.52.

Regarding the relationship between morphological aspects and impacts on aquatic ecosystems, all shapes and sizes of materials released into the environment exhibit distinctive morphology that is indicative of an original formation process. (Upstate Medical University, 2024). The results were surprising:

Particle morphology and particle size distribution. Marto et al.’s work defined the size distribution of CC particles as a Gaussian, monomodal, stable, and uniform distribution, while the particles’ size ranged from 1.76 ± 0.03 (d10) to 10.11 ± 0.70 μm (d90), with a main peak at 3.95 ± 0.09 μm. These results demonstrated that the CC particles were typically smaller than the target emulsion droplet size (Figure 2), allowing these micromolar-sized particles to be effectively injected into the emulsion with a high interface stability level.

In-vitro cytotoxicity results. The research group evaluated the hypothetical cytotoxicity of the studied objects in vitro by determining the viability of HaCaT cells using the MTT assay. As a result, the cell viability of CC-stabilized emulsion and CC particles was 102 ± 18% and 69 ± 12%, respectively. The particles were thus concluded to be more cytotoxic than the emulsion. This difference may be due to the surface roughness of the CC particles, which can minimize the repulsive forces between the particles and the plasma membrane, inducing cellular injury. By injecting CC particles inside the emulsion structure, this effect was decreased in the stabilized emulsion, as long as it was kept stable.

How could these results be related to the materials’ impacts on aquatic ecosystems?

Marto et al. did not analyze the environmental impacts of calcite particles and finished emulsions in their study, so findings from another research group can be reasonably considered. Spataru et al. reported that the toxicities of surfactants vary widely over several orders of magnitude, but in the presence of suspended carbonate particles, these surfactants manifest a specific behavior. The group argued that several processes, including the absorption of suspended solids, determine the environmental fate of organic pollutants in wastewater. It is known that surfactants from pesticides have polluted the natural water supply in recent decades, leading to the high solubilization of other oil-soluble pollutants such as DDT and trichlorobenzene (Lechuga et al., 2015). Although oil-surfactant mixtures are consistently more toxic than expected, the influence of pesticides and metal ions on surfactant toxicity is virtually uncertain. Consequently, the extrapolation of such complex data is difficult to complete. Simultaneously, Scott and Jones (2000) suggested that the cytotoxicity of various cationic mono-alkyl and di-alkyl quaternary ammonium salts significantly surpasses that of anionic and nonionic surface-active substance (SAS) builders.

Increased water hardness and temperature typically lead to higher surfactant toxicity. Many authors have investigated the adsorption of cationic and anionic surfactants on carbonates (Ma et al., 2013; Ying, 2005). The presence of suspended solid particles and naturally occurring dissolved substances decreases the bioavailability of cationic surfactants but not that of anionic and nonionic ones (Lechuga et al., 2016; Thomas et al., 2009).

Taking a case study of the Nistru River, downstream of Soroca town (Varancau, Moldavia), polluted with pesticides via runoff from storm drains and sewage pipes, Spataru et al. well studied the influence of carbonate particles on the nitrification process, which is the oxidation of nitrite ([NO2-]) to nitrate?([NO3-]) ions. The presence of cationic detergents (Sandu et al., 2007) can demonstrate the difference between the samples from the Nistru River in the villages of Varancau and Cunicea in terms of CC particles’ impact (Figure 3). In the sample without the carbonate substrate, nitrification is significant, obtaining high concentrations (12–14 mg/L) of nitrites. The formation of considerable quantities of nitrites shows that in a duration of 20 days, the rate of oxidation of ammonia and the nitrate-to-nitrite reduction exceed the nitrite ion oxidation of [NO2-] to?[NO3-]. The oxidation of ammonium ([NH4+ ]) ions is stopped in the sample with calcium carbonate CC particles. The [NO2-] ion concentration is 0.4 mg/L, while that of [NO3-] ions remains negligible in the analyzed sample within the studied period of time. Meanwhile, the concentrations of [NH4+] and [NO2-] ions in the river in Cunicea village, whose waters contain no synthetic surfactant, and the oxidation of ammonia are identical in samples with and without CaCO3. Therefore, it is assumed that the calcite particles can vigorously provoke the natural nitrification process, thus significantly calcifying the aquatic environment.?

What is the conclusion we have here?

The results effectively demonstrated that the calcite particles have proven to be relatively toxic to human cells compared to the calcite-based emulsion. However, keeping the emulsion products sufficiently safe for consumers is not a simple task, as they must be firmly stable and cannot be disintegrated into highly cytotoxic particles. When it comes to their environmental fate, the calcite ingredients are substantially associated with an ability to disrupt the nitrification process within a freshwater ecosystem. However, there is a need to put extra effort into studying the particles’ biological effects within vast ranges of natural biomes (in air, soil, or water).

How can cosmetic companies overcome the problems associated with calcite-based products?

As the public has become increasingly concerned about the toxicity of calcite ingredients over the years, it would be reasonable for cosmetic manufacturers to seek out alternatives to calcite. Reportedly, Make Vegan Makeup stated that silicones are able to effectively replace calcite ingredients while fabricating skincare products. The Skynth Research’s database has suggested certain types of sustainable silicones, including:

(a) Dimethicone and cyclomethicone are both made from dimethyldichlorosilane, which is made from powdered silicon (silicon dioxide) and methyl chloride. Dimethyldichlorosilane is then hydrolyzed to give a hydrolysate of polysiloxanes. In a polymerization reaction with water, the polysiloxanes are polymerized into linear silicone polymers to become dimethicone with different chain lengths. Meanwhile, polymerizing the polysiloxanes into a cyclic polymer will create cyclomethicone, which consists of either four (cyclotetrasiloxane) or five siloxane units (cyclopentasiloxane).

(b) Polymethylsilsesquioxane is used to form methyltrimethoxysilane, which is then polymerized by hydrolysis and condensed into polymethylsilsesquioxane.

They are functioning to improve skin feel and allow pigments to be dispersed with high water-resistance and film-forming ability.

What should consumers do to support the cause??

European researchers have emphasized the important role of consumers in the development of any product, and calcite-based cosmetics are no exception. Although calcite has been deemed “low risk” to human health and the environment in the INCI list, one must be aware that a number of databases are outdated and not always openly accessible to the public. Therefore, it would be worthwhile to consult the expert’s advice on the safety of using mineral-based products such as calcite. On top of that, as our former researcher, Tries Apriliando, indicated the damages caused by calcite exploration would be profound to the world’s biosphere heritages, it is thus our responsibility to preserve such treasures just by minimizing the consumption of any goods made from calcium carbonate. Let's seek out stably-structured silicones and encourage our scientific communities to further improve the quality of these ingredients for the sake of generations to come!

REFERENCES

Lechuga, M., Fernández-Serrano, M., Jurado, E., Nú?ez-Olea, J., & Ríos, F. (2015, November 30). Acute toxicity of anionic and non-ionic surfactants to aquatic organisms. PubMed. Retrieved March 5, 2016, from https://pubmed.ncbi.nlm.nih.gov/26650419/

Make Vegan Makeup. (2024, March 8). Learn all about cosmetic silicone and how to use them! Cosmetic Silicone. https://www.makeveganmakeup.com/cosmetic-silicone.html

Marto, J., Nunes, A., Martins, A. M., Carvalheira, J., Prazeres, P., Gon?alves, L., Marques, A., Lucas, A., & Ribeiro, H. M. (2020, July 9). Pickering Emulsions Stabilized by Calcium Carbonate Particles: A New Topical Formulation. MDPI. https://www.mdpi.com/2079-9284/7/3/62

Mineral Technologies Inc. (2023, August). Calcium Carbonate Market Size, Trends, Growth & Forecast. ChemAnalyst. https://www.chemanalyst.com/industry-report/calcium-carbonate-market-687

Nationwide Research. (2017, November 9). Calcite Crystals Market Research Report Unlocks Analysis on the Market Financial Status, Market Size, and Market Revenue upto 2030. LinkedIn. https://www.dhirubhai.net/pulse/calcite-crystals-market-research-report-unlocks-analysis-mclfc/

Scott, M., & Jones, M. (2000, February 9). The biodegradation of surfactants in the environment. Biochimica et Biophysica Acta (BBA) - Biomembranes. Retrieved January 3, 2023, from https://linkinghub.elsevier.com/retrieve/pii/S0304415700000137

Spataru, P., Fernandez, F., Sista, J., Spataru, T., Spinu, O., & Povar, I. (2017, June 6). Influence of the interaction of calcium carbonate particles with surfactants on the degree of water pollution in small rivers - Ecological Processes. Ecological Processes. Retrieved March 4, 2024, from https://ecologicalprocesses.springeropen.com/articles/10.1186/s13717-017-0086-4

Sun, C., Hu, K., Mu, D., Wang, Z., & Yu, X. (2022). The Widespread Use of Nanomaterials: The Effects on the Function and Diversity of Environmental Microbial Communities. MDPI. Retrieved September 22, 2022, from https://www.mdpi.com/2076-2607/10/10/2080

Tate, D. (2024, March 11). CALCIUM CARBONATE - Cosmetics Ingredient INCI. Cosmetics Ingredients. https://cosmetics.specialchem.com/inci-ingredients/calcium-carbonate

Upstate Medical University. (2024, March 5). Particle Morphology | Particle Analysis | SUNY Upstate Medical University. Upstate Medical University. https://www.upstate.edu/pathenvi/basics/particle_morphology.php