The cosmetic industry is among the first adaptors of nanotechnology through the use of engineered nanoparticles (ENPs) to enhance the performance of their products and meet the customers' needs. Recently, there have been increasing concerns from different societal stakeholders (e.g., governments, environmental activist pressure groups, scientists, general public, etc.) concerning the safety and environmental impact of ENPs used in cosmetics. This review paper seeks to address the twin concerns of the safety of cosmetics and the potential environmental impacts due to the constituent chemicals—the ENPs. The safety aspect is addressed by examining recently published scientific data on the possibility of ENPs penetrating human skin. Data indicates that although particular types of ENPs can penetrate into the skin, until now no penetration has been detected beyond the stratum corneum of the ENPs used in cosmetics. Yet, important lessons can be learned from the more recent studies that identify the characteristics of ENPs penetrating into and permeating through human skin. On the part of the environmental impact, the scientific literature has very limited or none existent specific articles addressing the environmental impacts of ENPs owing to the cosmetic products. Therefore, general ecotoxicological data on risk assessment of ENPs has been applied to ascertain if there are potential environmental impacts from cosmetics. Results include some of the first studies on the qualitative and quantitative risk assessment of ENPs from cosmetics and suggest that further research is required as the knowledge is incomplete to make definitive conclusions as is the case with skin penetration. The authors conclude that the cosmetic industry should be more transparent in its use of nanotechnology in cosmetic products to facilitate realistic risk assessments as well as scientists and pressure groups being accurate in their conclusions on the general applicability of their findings. Transparency in cosmetics needs nanotechnology, but nanotechnology in cosmetics also needs transparency

Nanotechnology is currently at the forefront of scientific research and technological developments that have resulted in the manufacture of novel consumer products and numerous industrial applications using engineered nanomaterials (ENMs). With the increasing number of applications and uses of ENMs comes an increasing likelihood of nanoscale materials posing potential risks to the environment and engineered technical systems such as wastewater treatment plants (WWTPs). Recent scientific data suggests that ENMs that are useful in, for example, medical applications due to their novel physicochemical properties, may also cause adverse effects to the bacterial populations used in wastewater treatment systems. In this review, the toxicological effects of titanium nanoparticles (nTiO₂), zinc oxide (nZnO), carbon nanotubes (CNTs), fullerenes (C₆₀) and silver nanoparticles (AgNPs) to bacteria were examined. The results suggest that the potential ENMs risks to bacteria are non-uniform (need to be assessed case-by-case), and are dependent on numerous factors (e.g. size, pH, surface area, natural organic matter). Currently available data are therefore insufficient for evaluating the risks that ENMs pose in WWTPs. To fill these knowledge gaps, we recommend scenario specific studies aimed at improving our understanding on: (i) estimated volumes of ENMs in effluents, (ii) the antibacterial sensitivity of cultures within WWTPs towards selected ENMs, and (iii) processes improving the stability of ENMs in solutions. Two factors that merit consideration for elucidating the potential risks systematically are the toxicity mechanisms of ENMs to bacteria, and the influencing factors based on inherent physicochemical properties and environmental factors. Furthermore, the complexity of behaviour and fate of ENMs in real WWTPs requires case studies for assessing the ENMs risks to bacteria in vivo. The current laboratory results derived using simplified exposure media do not reflect actual environmental conditions.

The toxicity effects of silver (nAg) and zinc oxide (nZnO) engineered nanoparticles (ENPs) on the duckweed Spirodela punctuta were studied to investigate the potential risks posed by these ENPs towards higher aquatic plants. The influence of media abiotic factors on the stability of the ENPs was also evaluated. Marked agglomeration of ENPs was observed after introduction into testing media whereby large particles settled out of suspension and accumulated at the bottom of testing vessels. The high ionic strength (IS) promoted agglomeration of ENPs because it reduced the inter-particle repulsion caused by a reduction in their surface charge. Low dissolution was observed for nAg, reaching only 0.015% at 1000 mg L⁻¹, whilst improved dissolution was observed for nZnO, only falling below analytical quantification at 0.1 mg L⁻¹ and lower. The quantification of free radicals namely, reactive oxygen and nitrogen species (ROS/RNS) and hydrogen peroxide (H₂O₂), indicated the induction of oxidative stress in plants exposed to the ENPs. A definite dose influence was observed for ROS/RNS volumes in plants exposed to nZnO for 14 days, a response not always observed. The total antioxidant capacity (TAC) and superoxide dismutase (SOD) activity in plants indicated varying degrees of oxidative toxicity caused by exposure to ENPs. This toxicity was driven mainly by particulates in plants exposed to nAg, whilst dissolved Zn²⁺ was the main driver for toxicity in plants exposed to nZnO. Our findings suggest that the toxicity of nAg and nZnO could be caused by both the particulates and ionic forms, as modified by media properties.

This paper attempts to quantify the potential risks posed by engineered nanomaterials (ENMs) to the aquatic and terrestrial ecosystems from cosmetic-based nanoproducts. The predicted environmental concentrations (PEC) were modelled for the silver (nAg) and titanium dioxide (nTiO₂) nanoparticles embedded in cosmetic nanoproducts. The Johannesburg Metropolitan City (JHB City), in South Africa, was used as the reference study area. A mathematical model was applied to compute the quantities of ENMs flows from the cosmetic nanoproducts into the JHB City aquatic and terrestrial ecosystems. The risk quotient (RQ) of the nanoscale materials were evaluated as a ratio of PEC to the predicted no effect concentrations (PNEC). RQ values showed wide variance due to factors like; the quantities of ENMs, the fate and pathways of ENMs in the aquatic and terrestrial ecosystems, efficiency of the wastewater treatment plants (WWTP) as well as the economic and demographic data for South Africa and Switzerland. For the aquatic environment, the PEC values of nAg ranged from 2.80 × 10⁻³ to 6.19 × 10⁻¹ μg L⁻¹ whereas for nTiO₂ the values ranged from 2.7 0 × 10⁻³ to 2.70 × 10⁻¹ μg L⁻¹ under the realistic dilution factor of 1 with the WWTP functioning at high removal efficiency regime. The RQ values in the aquatic ecosystems were mostly >1, indicating the potential risk of both nAg and nTiO₂ but <<<1 in the terrestrial ecosystems. Our results provide the first quantification of ENMs potential risk into the environment Johannesburg City in a developing country’s natural and technical settings.