Plastics are widely used in daily life due to their excellent properties, such as lightweight nature, high durability, and ease production, and versatility (Wang et al., 2022a; Zeb et al., 2024a). However, this widespread usage has resulted in a surge of plastic waste. By 2015, approximately 5000 Mt of plastic ended up either in landfills or was introduced in the natural environment, and this number is projected to escalate to 12,000 Mt by 2050 (Geyer et al., 2017). The global reliance on plastics has led to their widespread diffusion and accumulation as debris in both terrestrial and aquatic environments (Dainelli et al., 2023). When larger plastic debris ages and degrades, it breaks down into smaller particles known as microplastics (MPs) if they measure less than 5 mm (Lian et al., 2022; Cao et al., 2023; Xu et al., 2023), or nanoplastics (NPs) if they are smaller than 1 μm (Lian et al., 2021; Wang et al., 2022a; Dainelli et al., 2023). Due to their widespread presence and continuous accumulation in the environment, they have been recognized as one of the emerging contaminants (Lian et al., 2022).

Although the magnitude of microplastic pollution on land is estimated to be 4–23 times higher than that in the oceans (Horton et al., 2017), terrestrial systems receive much less attention than aquatic environments (de Souza Machado et al., 2018b, de Souza Machado et al., 2018a). Soil serves as an important sink for varying types, sizes, and quantities of microplastics deposited in terrestrial ecosystems globally ( Li et al., 2021a; Cao et al., 2023). Among these ecosystems, agricultural environments have been identified as one of the most affected areas (Lian et al., 2020a, 2022; Dainelli et al., 2023; Zeb et al., 2024a). Some studies have estimated that the total annual input of MPs into farmlands in Europe and North America were 63,000–430,000 tons and 44,000–300,000 tons, respectively (Nizzetto et al., 2016). In Australia, between 2800 and 19,000 tons of MPs enter the agro-ecosystems through bio-solids each year (Ng et al., 2018). In China, the concentration of microplastics in farmland soils ranges from 48 n/kg to 7579 n/kg, with the highest and lowest concentrations observed in the marginal tropical humid area and semi-arid plateau temperate area, respectively (Cai et al., 2023). MPs enter agricultural soils mainly through membrane mulching, sewage sludge, greenhouse materials, and atmospheric deposition (Li et al., 2021b; Wang et al., 2022b; Lian et al., 2022, 2024).

Sewage sludge, commonly utilized as a fertilizer in agricultural systems (de Souza Machado et al., 2018b; Ali et al., 2023), is considered a significant source of MPs in terrestrial ecosystems. MPs from biosolids often contain substantial amounts of clothing fibers or particles from personal care products, and this way they are also being introduced into the farmland soil (Lian et al., 2020a; Dainelli et al., 2023). Numerous studies have demonstrated the significant impact of microplastics on agricultural ecosystems, manifesting in various aspects (Lian et al., 2022; Pérez Reverón et al., 2022; Dainelli et al., 2023). These effects include alterations in soil physicochemical properties (Ge et al., 2021; Liu et al., 2022; Wang et al., 2022b), disturbances in soil microbial community structure and function (de Souza Machado et al., 2018a; Li et al., 2021b; Sarkar et al., 2022) or increasing the bioavailability of coexisting pollutants in the soil, such as heavy metals (HMs) (Wang et al., 2020a, 2021a). As shown in Fig. 1, the infiltration of multiple contaminants into plants can severely adversely affect crop quality, posing a threat to human health through the food chain and interconnected food webs (Hartmann et al., 2022; Pérez-Reverón et al., 2022; Dainelli et al., 2023).

The interaction between microplastics and heavy metals present in the same environment has attracted significant attention in recent studies. Cao et al. (2023) and Wang et al. (2022a) have reported that microplastics in soil can serve as carriers of heavy metals, thereby significantly affecting their bioavailability. Wang et al. (2020a) was early to highlight the threat of combined MPs-HMs pollution to crop safety, and studied its effect on maize crops. Several recent studies have suggested that the combined contamination may exert more severe inhibitory effect on plant growth (Yoon et al., 2021; Liu et al., 2023). More importantly, the increased accumulation of MPs and HMs in plants may pose a threat to human health through the food chain (Jia et al., 2022; Xu et al., 2023). The quality of terrestrial plants, especially crops, is closely related to human health. While several reviews have delved into the individual effects of microplastics on plants (Maity and Pramanick, 2020; Chen et al., 2022; Wang et al., 2022a; Wang et al., 2022c), there is a scarcity of studies that comprehensively review the effects of heavy metals and microplastics on terrestrial plants. This gap limits the advancement of relevant research and practical engineering applications. Based on this, the articles of the present review were selected through literature search and retrieval from Web of Science, and then identified studies that meeting the criteria. The key words, i.e., “microplastics AND heavy metals AND soil”, “microplastics AND heavy metals AND plants” and “microplastics AND heavy metals” were used to search. The titles, abstracts, and conclusions of the retrieved articles, as well as the content of their chapters, were carefully scrutinized. Due to the scarcity of relevant articles, we also inspected the references of the selected articles to identify additional ones pertinent to the content of this review. Overall, there are relatively few studies related to the content of this review, totaling only 22 articles. Most of the selected test plants were crops and vegetables. Among heavy metal pollutants, Cd attracted the most attention with 12 related studies; followed by As, with 8 studies; and Pb, with 5 studies. Regarding microplastics, PE-MPs are the most studied, with 11 related studies; followed by PE-MPs with 6 studies; and PTFE-MPs with 3 studies. The aims of the present review are to enhance our understanding of the fate and toxicity of combined contaminants (MPs and HMs) to terrestrial plants and investigate its environmental impacts. The present study reviews the effects of these combined pollutants on the physicochemical properties, microorganisms, and enzyme activities of rhizosphere soil. Furthermore, the review analyzes the response of plant growth and biochemical indicators to the presence of combined pollutants, along with the plants’ pathway and capability to accumulate these contaminants. Ultimately, the areas of further studies that should be carried out was recommended. Overall, this review contributes to our knowledge of the impact and mechanism of combined pollutants on terrestrial plants’ growth, as well as the potential environmental toxicity risks.