Jun-Kit Wan

There has been increasing concern over the toxic effects of microplastics (MP), nanoplastics (NP), and copper (Cu) on microalgae. However, the combined toxicity of the metal in the presence of polystyrene (PS) MP/NP on microalgae has not been well studied, particularly after long-term exposure (i.e., longer than 4 days). The primary aim of the present study was to investigate the effect of PS MP and NP on Cu toxicity on two freshwater microalgae, namely Chlorella sp. TJ6-5 and Pseudokirchneriella subcapitata NIES-35 after acute exposure for 4 days and up to 16 days. The results showed that both microalgae were sensitive to Cu, but tolerant to MP/NP. However, MP/NP increased the toxicity of Cu at EC₅₀ in both microalgae, which was only noticeable in chronic exposure. Single and combined treatment of MP/NP and Cu induced higher oxidative stress and caused morphological and ultrastructural changes in both microalgae. The adsorption of Cu to MP and NP was low (0.23–14.9%), with most of the Cu present in free ionic form (81.6–105.8%). The findings on different sensitivity of microalgae to Cu in the presence of MP/NP may have significant implication as microalgae are likely to be exposed to a mixture of both MP/NP and Cu in the environment. For example, in air-blasting technology, MP and NP are used as abrasive medium to remove Cu-containing antifouling paints on hulls of ship and submerged surfaces. Wastewater treatment plants receive household wastes containing MP and NP, as well as stormwater runoffs and industrial wastes contaminated with heavy metals.

Plastics, with their many useful physical and chemical properties, are widely used in various industries and activities of daily living. Yet, the insidious effects of plastics, particularly long-term effects on aquatic organisms, are not properly understood. Plastics have been shown to degrade to micro- and nanosize particles known as microplastics and nanoplastics, respectively. These minute particles have been shown to cause various adverse effects on aquatic organisms, ranging from growth inhibition, developmental delay and altered feeding behaviour in aquatic animals to decrease of photosynthetic efficiency and induction of oxidative stress in microalgae. This review paper covers the distribution of microplastics and nanoplastics in aquatic ecosystems, focusing on their effects on microalgae as well as co-toxicity of microplastics and nanoplastics with other pollutants. Besides that, this review paper also discusses future research directions which could be taken to gain a better understanding of the impacts of microplastics and nanoplastics on aquatic ecosystems.