لخّصلي

Plastic is an essential component of modern life and is utilized in various aspects of our daily routine, including packaging, household items, and clothing.In the present review article, we aim to address a research gap by discussing the impact of interactions between MPs and other contaminants in various sludge treatment processes.Primary MPs, such as microbeads from cosmetics and personal care products, and secondary MPs from laundry and industrial sources are also significant contributors of hazardous heavy metals and organic contaminants (Bretas Alvim et al., 2020; Li et al., 2018).Approximately 50%-80% of heavy metals (i.e., Cu, Zn, Pb, Cr, Ni, Cd, Hg, and Mn) in sewage enter SS via physicochemical and biological interactions (Yang et al., 2020).Wagstaff et al. (2022) confirmed the capacity of MPs to adsorb pharmaceuticals, with greater affinity observed for more hydrophobic compounds (log DOW >= 1.65) that were found to adsorb to polyamide (nylon) MPs in wastewater at pH 7.6.The accumulation of MPs can also impact aquatic organisms, resulting in reduced feeding activity, oxidative stress, genotoxicity, growth retardation, and mortality (Carlos et al., 2018; Hernandez-Arenas et al., 2021; Shiu et al., 2020b).These small plastic particles have infiltrated aquatic, terrestrial, and atmospheric environments, posing a significant threat to both wildlife and humans (Li et al., 2020; Ni'am et al., 2022; Shiu et al., 2021).Although WWTPs are not specifically designed to treat MP pollutants in wastewater, previous studies indicate that there is a reduction in the concentration of MPs between the influent and effluent wastewater streams.MPs can also originate from the degradation of plastic products due to mechanical, photo-oxidative, and other effects, resulting in the release of fragments and dust particles; these are known as secondary MPs (Murphy et al., 2016; Shiu et al., 2022).WWTP sludge as a fertilizer in agriculture has gained popularity due to its high amount organic and nutrient contents (Wagstaff et al., 2022).

Plastic is an essential component of modern life and is utilized in various aspects of our daily routine, including packaging, household items, and clothing. This widespread plastic use has had severe environmental consequences. Plastic production has increased significantly in recent decades, with an estimated 300 million tons of plastic produced worldwide each year (Huang et al., 2021; Reddy and Nair, 2022). The impact of this mass production has been devastating, with a significant concern being the generation of microplastics (MPs). These small plastic particles have infiltrated aquatic, terrestrial, and atmospheric environments, posing a significant threat to both wildlife and humans (Li et al., 2020; Ni’am et al., 2022; Shiu et al., 2021). The term ‘‘micro–nano plastics’’ (M-NPs) was first introduced by Thompson et al. (2004). MNPs are defined as plastics smaller than 5 mm and include plastic particles, fragments, fibers, and other similar materials (Thompson et al., 2004).
MPs are considered to be emerging pollutants and can originate from various sources (Shiu et al., 2020a). One source is plastic microbeads, which are commonly used in personal care products and industrial processes (Gatidou et al., 2019). Another is the breakdown of textile fibers that are discharged from laundry machines, which are known as primary MPs (Galvão et al., 2020; Yadav et al., 2023). MPs can also originate from the degradation of plastic products due to mechanical, photo-oxidative, and other effects, resulting in the release of fragments and dust particles; these are known as secondary MPs (Murphy et al., 2016; Shiu et al., 2022). Wastewater, which includes domestic waste, flows through the sewerage system to wastewater treatment plants (WWTPs) and is treated before discharge into water bodies. WWTPs act as collection points for various contaminants, one of which is MPs (Ben-David et al., 2021). Although WWTPs are not specifically designed to treat MP pollutants in wastewater, previous studies indicate that there is a reduction in the concentration of MPs between the influent and effluent wastewater streams. This reduction can vary depending on the treatment unit, with reported reductions ranging from 58.8% to 99.9% (Cristaldi et al., 2020; Liu et al., 2021; Xu et al., 2021). According to research conducted by Ziajahromi et al. (2021), approximately 79% of the MPs that enter WWTPs will end up in the sludge phase or in biosolids, which may be disposed of in landfills or further processed. According to the literature, the amount of MPs in sludge from WWTPs worldwide ranges from >1,000 particles kg−1 to 301,400 particles kg−1 (Nguyen et al., 2022). In a study conducted in China, an average of 10,280 particles kg−1 with various shapes (such as granular or fibrous) as well as films and fragments were found (Yuan et al., 2022). MPs in sewage sludge (SS) are mainly derived from industry applications and washing activity (Li et al., 2018).
The presence of MPs in WWTP sludge is a growing concern due to the potential risks and the accumulation loading of MPs and others contaminant (Chen et al., 2020; Sadia et al., 2022). Not only do MPs add to the list of contaminants, they also increase the potential for interactions with other pollutants. Research conducted by Mahon et al. (2017) showed that the treatment process in WWTP can cause changes in the size of MPs. Other studies showed that MPs can accumulate in sewage sludge, potentially transporting other contaminants (Huang et al., 2021). The accumulation of MPs in sludge poses a risk to human and environmental health. When sludge is applied to land, the MPs can leach into the soil, potentially affecting soil health and contaminating crops. Furthermore, sludge may be incinerated, releasing MPs into the atmosphere (Shi et al., 2022a). There is a need for further research into the potential risks associated with MPs in WWTP sludge. Approximately 50%–80% of heavy metals (i.e., Cu, Zn, Pb, Cr, Ni, Cd, Hg, and Mn) in sewage enter SS via physicochemical and biological interactions (Yang et al., 2020). MPs also have the potential to absorb heavy metals (Ashton et al., 2010). Researchers have investigated the hydrophobic surfaces of MPs and discovered that they can attract various types of organic matter, biomolecules, and bacteria. The bacteria that adhere to MPs are of particular interest, as they may be microbial pathogens that could be harmful to human health and potentially resistant to antimicrobial treatment (Bowley et al., 2021; Kaur et al., 2022). Wagstaff et al. (2022) confirmed the capacity of MPs to adsorb pharmaceuticals, with greater affinity observed for more hydrophobic compounds (log DOW ≥ 1.65) that were found to adsorb to polyamide (nylon) MPs in wastewater at pH 7.6. In recent years, numerous studies have been published demonstrating the existence of MPs in SS. This discovery should heighten concerns regarding the management of sludge containing MPs (Hatinoğlu and Sanin, 2021).
WWTP sludge as a fertilizer in agriculture has gained popularity due to its high amount organic and nutrient contents (Wagstaff et al., 2022). However, the application of SS and compost fertilizer in agriculture has also been identified as one of the primary sources of MPs contamination in soil (Bläsing and Amelung, 2018). The accumulation of MPs can also impact aquatic organisms, resulting in reduced feeding activity, oxidative stress, genotoxicity, growth retardation, and mortality (Carlos et al., 2018; Hernández-Arenas et al., 2021; Shiu et al., 2020b). Primary MPs, such as microbeads from cosmetics and personal care products, and secondary MPs from laundry and industrial sources are also significant contributors of hazardous heavy metals and organic contaminants (Bretas Alvim et al., 2020; Li et al., 2018).
Very few critical reviews are available that deal specifically with MPs SS; the majority of the existing reviews address MPs in wastewater and their impact on the aquatic environment (Cristaldi et al., 2020; Gkatzioura et al., 2021; Liu et al., 2021; Sadia et al., 2022). Some reviews specifically discuss the presence of MPs in sludge in relation to identification, enumeration, and characterization methods, such as that conducted by Christian and Köper (2023). In the present review article, we aim to address a research gap by discussing the impact of interactions between MPs and other contaminants in various sludge treatment processes. Specifically, we examine the influence of these interactions on the resulting sludge treatment products, as well as their potential effects on the environment and human health. It is worth noting that each sludge treatment process is characterized by distinct objectives and physical and chemical treatment conditions, which may exacerbate the interaction between MPs and other contaminants.