Microplastics in Agricultural Soils: A Case Study in Cultivation of Watermelons and Canning Tomatoes

Thirty soil samples were collected from fields that have been used for cultivating watermelons and canning tomatoes for over 10 years. The microplastics (MPs) within these samples were separated with a density floatation method and the use of sieves and filters. The microplastics found were black and originated from the black agricultural mulch film (BMF) used in these cultivations. ATR-FTIR spectroscopy revealed that these microplastics are of the same material as the virgin BMF and as a virgin polyethylene film used as blank. SEM images showed that used BMF and MPs found in soil were oxidized by their exposure to sunlight and create fibrous edges that lead to the creation of smaller size MPs. The number of MPs found in fields with watermelon (301 +/- 140 items kg(-1)) were more than four times higher than in fields with canning tomatoes (69 +/- 38 items kg(-1)) due to the double planting each year and to the second planting last year being closer to the sampling episode. All the sample sites were collected from agricultural fields away from the industrial area; therefore, these results prove that agricultural activities might have caused contamination of soils with MPs. This is corroborated even more by the fact that no MPs were found in five extra samples that were taken from uncultivated areas as blanks.

Automated summary

The study found that the soil samples from fields with watermelon cultivation had a higher concentration of microplastics compared to fields with canning tomatoes, due to double planting each year and the closer proximity of the second planting to the sampling time. All samples were collected from agricultural fields away from industrial areas, indicating that agricultural activities may have caused soil contamination with microplastics.