The transport of microplastics by ants cannot be neglected in the soil ecosystem

Microplastics (MPs) are widespread in soils and continue to migrate in response to many abiotic and biotic factors. Although some studies have explored the effects of abiotic factors (e.g., wind and water) on MP migration and distribution, there is little information on the effects of biotic factors, especially soil fauna, on this process. Ants are among the most abundant fauna on Earth and play an important role in ecosystem health. Here, we tested whether ants could transport low-density polyethylene (LDPE) MPs in the field. We also investigated the effects of ants (Pheidole sp.) on the removal rates and distribution of LDPE MPs in the laboratory compared to other potential field materials (leaf fragments and tiny stones). We found that, in the field, two ant species (Pheidole sp. and Paratrechina sp.) could actively carry LDPE MPs; the mean removal distance was 75.34 ± 4.05 cm, and the curve had a long tail extending to 140 cm. In the laboratory, the mean number of removed leaf fragments and LDPE MPs was significantly greater than that of removed tiny stones. After 14 days, the proportions of LDPE MPs, leaf fragments, and tiny stones removed into the nests by ants were 15.8%, 19.15%, and 3.3%, respectively. The proportions of LDPE MPs in the original position (not removed by ants), inside the nests, and outside the nests were 18.4%, 15.8%, and 65.8%, respectively. These results indicate that ants play an important, but neglected, role in the transport and distribution of MPs in soil ecosystems. Given the abundance and diversity of ants worldwide, the ant-mediated transport of MPs may be common in soil ecosystems. We suggest that the transport of MPs by ants may expand the distribution of MPs and influence the exposure of other soil fauna to MPs in soil ecosystems.