Microplastic contamination in the agricultural soil-mitigation strategies, heavy metals contamination, and impact on human health: a review.

Microplastic pollution has emerged as a critical global environmental issue due to its widespread distribution, persistence, and potential adverse effects on ecosystems and human health. Although research on microplastic pollution in aquatic environments has gained significant attention. However, a limited literature has summarized the impacts of microplastic pollution the agricultural land and human health. Therefore, In the current review, we have discussed how microplastic(s) affect the microorganisms by ingesting the microplastic present in the soil, alternatively affecting the belowground biotic and abiotic components, which further elucidates the negative effects on the above-ground properties of the crops. In addition, the consumption of these crops in the food chain revealed a potential risk to human health throughout the food chain. Moreover, microplastic pollution has the potential to induce a negative impact on agricultural production and food security by altering the physiochemical properties of the soil, microbial population, nutrient cycling, and plant growth and development. Therefore, we discussed in detail the potential hazards caused by microplastic contamination in the soil and through the consumption of food and water by humans in daily intake. Furthermore, further study is urgently required to comprehend how microplastic pollution negatively affects terrestrial ecosystems, particularly agroecosystems which drastically reduces the productivity of the crops. Our review highlights the urgent need for greater awareness, policy interventions, and technological solutions to address the emerging threat of microplastic pollution in soil and plant systems and mitigation strategies to overcome its potential impacts on human health. Based on existing studies, we have pointed out the research gaps and proposed different directions for future research.

Effect of different types and shapes of microplastics on the growth of lettuce.

The presence of microplastics in agricultural soils has emerged as a significant environmental concern due to their persistent nature. Microplastics of different properties (i.e., types, shapes, size, concentration) are present in the environment, but the studies on the effect of microplastics having different properties are limited. Thus, this study investigated the effects of different microplastics (low-density polyethylene (LDPE) fragments, polyvinyl chloride (PVC) fragments, and LDPE fiber) in soil on the growth of lettuce (Lactuca sativa L.). Pot tests were carried out to study the effect of a range of microplastic concentrations and different shapes and types of microplastics in soil on the lettuce growth. The different growth parameters such as lettuce weight, lengths, and chlorophyll contents were measured and compared. The results showed that the adverse effects of the microplastics on the lettuce growth increased with increasing microplastic concentration. The effects of LDPE fragments and fibers on the root weights and the chlorophyll contents were microplastic shape-dependent. Also, the effects of LDPE fragments and PVC fragments on the shoot and root weights and the chlorophyll contents were microplastic type-dependent. Among the three microplastics studied, LDPE fragments tend to have greater effects on the lettuce growth than the other microplastics. Overall, the results show that the effects of microplastics on different growth parameters of lettuce can be shape- and/or type-dependent. The presence of microplastics having different properties make the understanding the effects of microplastics on plants difficult, and this necessitates further studies.

Responses of earthworms exposed to low-density polyethylene microplastic fragments.

The interest in the effect of microplastics (MPs) on the terrestrial environment has been increasing recently. Different species of earthworms have been used to study the effects of MPs on different aspects of earthworm health. However, there is still a need for more studies because different studies report different effects on earthworms depending on the properties (e.g., types, shapes, sizes) of MPs in the environment and exposure conditions (e.g., exposure period). This study used Eisenia fetida as a test earthworm species to investigate the effect of different concentrations of low-density polyethylene (LDPE) MPs (≤125 µm) in soil on the growth and reproduction of earthworms. The exposure of the earthworms to the different concentrations of LDPE MPs (0-3% w/w) for 14 d and 28 d neither caused death of the earthworms nor showed significant effects on the earthworm weights in this study. The number of cocoons produced by the exposed earthworms were also similar to that of the controls (i.e., no exposure to MPs). Some previous studies reported similar results to what have been observed in this study, while some studies reported different results. On the other hand, the number of ingested MPs by the earthworms increased with increasing MPs concentrations in soil, suggesting a potential for damage to digestive tract. Also, the earthworm skin surface was damaged after exposure to MPs. The ingested MPs and the skin surface damage suggest that there is a potential for adverse effects on the earthworm growth after a longer-term exposure. Overall, the results of this study show that the effects of MPs on earthworms need to be studied using various endpoints including growth, reproduction, ingestion, and skin damage and such effects can be different depending on the exposure conditions such as MPs concentration and exposure period.

Changes in the aquatic ecotoxicological effects of Triton X-100 after UV photodegradation.

Various spray adjuvants including surfactants are widely used in agricultural pesticide formulations, and some of them may remain in soils and waters and impose more adverse effects than active pesticide ingredients on organisms. However, previous studies are more focused on the active pesticide ingredients than the adjuvants. Thus, this study investigates the changes in toxic effects of surfactants during photodegradation, which is one way of naturally degrading contaminants in natural waters. Triton X-100, a water-soluble non-ionic surfactant, was degraded using different types of UV radiation (UVA, UVB, and UVC), and the changes in the toxic effects were determined using bioluminescent bacteria and water flea. The Triton X-100 removals were negligible with UVA within 24 h, while its removal was 81% with UVB and almost complete with UVC. The NMR spectra indicated possible molecule rearrangement after photolysis. On the other hand, the toxic effects based on the mortality of Daphnia magna and the bioluminescence of Aliivibrio fischeri increased (i.e., lower EC50 values) after photodegradation, suggesting the generation of photoproducts that are likely to have higher toxic effects or higher bioavailability. Furthermore, the sensitivities of D. magna and A. fischeri for Triton X-100 and the photodegraded Triton X-100 were different. This study suggests that the changes in the chemical composition of the Triton X-100 containing water with photodegradation can lead to changes in the relative toxic effects on different aquatic organisms. Therefore, not only the management of parent compound (i.e., Triton X-100) but also the photoproducts generated from the parent compound need to be considered when managing water environment subject to photodegradation.