Table 1.

Summary of toxicological studies of microplastics (MPs) exposure on plants

Matrix studied	MPs type	Treatment	Plant studied	Plant part	Result	Conclusion	References
Soil	Bio and LDPE	1 % with and without earthworm	wheat (Triticum aestivum)	Above- ground	Bio-affected above ground biomass negatively reducing plant height, number of tillers, fruits and causing thinner stem during the growth process while LDPE showed no clear effect in comparison with control.	Earthworm had a positive effect on the wheat growth and chiefly alleviated the impairments made by plastic residues increasing total biomass by 26.2% after 4 months. However, both Bio and LDPE significantly affected the total biomass.	[13]
				Below-ground	Significant decrease in below-ground biomass
	Synthetic fibre, Bio-PLA and HDPE	0.001% w/w, 0.1 % w/w and 0.1 % w/w respectively.	perennial ryegrass (Lolium perenne)	Above-ground	Shoot height was reduced especially for synthetic fibre and Bio-PLA. Increased chlorophyll a and b contents compared to control.	The study provided evidence that MPs manufactured of HDPE. PLA, and synthetic fibers can affect the development of L. perenne health	[56]
				Below-ground	Seed germination was reduced especially for synthetic fibre and Bio-PLA. Increased root biomass compared to control except bio-PLA
	LDPE, PP and PS	0.5 % w/w (LDPE, PP, PS respectively), 1 % w/w (for LDPE+PP, LDPE+PS, PP+PS respectively) and 1.5 % w/w (LDPE+PP+PS)	Juvenile Lime Tree (Citrus aurantium)	Above ground	Showed more negative effects compared to control by reducing height, number of branches, leaf number and area. Highest negative effect shown by LDPE while least by LDPE+PP+PS	C.aurantium generally showed high tolerance (>70%) to the different treatment groups. Despite the observed toxicity symptoms as the decrease in total plant biomass, there was no unfavorable impact on the relative growth rate (RGR) of the tree.	[57]
	Green fluorescent Microspheres	103 to 107 Particles/mL	vascular plant (Lepidium sativum)	Below-ground	Reduced germination after 8 hours of exposure with no significant differences after 24 hours from the control	Increasing exposure concentration, size and time reduces germinating rate and chlorophyll contents.	[80]
Sediment	PS	10 % dry weight	M. spicatum Elodea sp.	Above-ground	Shoot length reduced with increasing concentration	All effects occurred at higher than environmentally realistic concentrations, suggesting no immediate implications for ecological risks.	[81]
Water	PE Microbeads	0, 10, 50, and 100 mg/L	duckweed (L. minor)	Root	Significant decrease in root length with increasing concentration	Overall, results showed that specific leaf growth rate and content of photosynthetic pigments in duckweed leaves are not negatively affected by polyethylene microbeads. However, investigated particles significantly affected the root growth	[58]
				Leaves	After seven days treatment caused less than 10% inhibition in comparison to control (<8%) with no significant effect. Furthermore, photosynthetic pigment concentration (chlorophyll a and b) was not significantly affected compared to controls
	PE	50,000 MPs/mL	duckweed (L. minor)	Root	Root length increased with time from 24 to 168 hours with no significant differences from the control	Over seven days PE MPs did not affect photosynthetic efficiency and plant growth. However, 30-day chronic exposure showed some negative effect on root and leaves.	[27]
				Leaves	Photosynthetic pigment concentration (chlorophyll a and b) was not significantly affected compared to controls
	PS-MPs	5 μm with 10, 50 and 100 mg/L	Vicia faba	Whole plant	Reduced growth with varying effect on enzyme activities such as catalase (CAT) (decreased significantly), superoxide dismutase (SOD) and peroxidase (POD) (both increased significantly).	Showed mild genotoxic effects on the plant and most probably block cell connections or cell wall pores for transport of nutrients.	[82]

^*Bio: Biodegradable; PLA: polylactic acid, HDPE: high density polyethylene, PP: polypropylene, PS: polystyrene, LDPE: low density polyethylene.