Sources of light density microplastic related to two agricultural practices: The use of compost and plastic mulch

Microplastics (MPs) constitute a known, undesirable contaminant of the ecosystems. Land-based pollution is considered to be an important contributor, but microplastics in the terrestrial environment remains largely unquantified. Some agriculture practices, such as plastic mulch and compost application, are suspected to be major sources of microplastics as plastics are exposed to weathering or are present in organic fertilizers. The overall aim of this research is to bridge the terrestrial plastic contamination information gap, focusing on light density microplastics in two vegetable production systems in Southeast Spain and in the Netherlands. The selected farmer in Spain used plastic mulch for more than 12 years whereas the two farmers in the Netherlands annually applied 10 t ha compost for the past 7 and 20 years. Samples from two different depths were collected: 0–10 cm and 10–30 cm. High quality compost samples originating from municipal organic waste and from garden and greenhouse waste were obtained from two Dutch compost plants. All samples from both Spanish (n = 29) and Dutch (n = 40) soils were contaminated by microplastics, containing 2242 ± 984 MPs kg and 888 ± 500 MPs kg, respectively. Compost samples from municipal organic waste (n = 9) were more contaminated than the ones from garden and green house wastes (n = 19), with, respectively, 2800 ± 616 MPs kg and 1253 ± 561 MPs kg . These results highlight the need for studies focusing on the effects of microplastics in the environment and the need for monitoring campaigns and the implementation of thresholds to regulate the microplastic contamination.