Farmland soils are prone to contamination with micro- and nanoplastics through a variety of agricultural practices. Concerns are recurrently raised that micro- and nanoplastics act as vector for organic contaminants to deeper soil layers and endanger groundwater resources. Whether and to what extent micro- and nanoplastics facilitate the transport of organic contaminants in soil remains unclear. Here we calculated the ratio between transport and desorption time scales using two diffusion models for micro- and nanoplastics between 100 nm and 1 mm. To identify micro- and nanoplastics bound contaminant transport we evaluated diffusion and partitioning coefficients of prominent agrochemicals and additives and of frequently used polymers e.g., polyethylene and tire material. Our findings suggest that the desorption of most organic contaminants is too fast for micro- and nanoplastics to act as transport facilitators in soil. Contaminant transport enabled by microplastics was found to be relevant only for very hydrophobic contaminants (logKow >5) under preferential flow conditions. While micro- and nanoplastics might be a source of potentially harmful contaminants in farmland soils this study suggests that they do not considerably enhance contaminant mobility.
Phthalic acid esters
(phthalates) have been detected everywhere
in the environment, but data on leaching kinetics and the governing
mass transfer process into aqueous systems remain largely unknown.
In this study, we experimentally determined time-dependent leaching
curves for three phthalates di(2-ethylhexyl) phthalate, di(2-ethylhexyl)
terephthalate, and diisononyl phthalate from polyvinyl chloride (PVC)
microplastics and thereby enabled a better understanding of their
leaching kinetics. This is essential for exposure assessment and to
predict microplastic-bound environmental concentrations of phthalates.
Leaching curves were analyzed using models for intraparticle diffusion
(IPD) and aqueous boundary layer diffusion (ABLD). We show that ABLD
is the governing diffusion process for the continuous leaching of
phthalates because phthalates are very hydrophobic (partitioning coefficients
between PVC and water log K
PVC/W were
higher than 8.6), slowing down the diffusion through the ABL. Also,
the diffusion coefficient in the polymer DPVC is relatively
high (∼8 × 10–14 m2 s–1) and thus enhances IPD. Desorption half-lives of
the studied PVC microplastics are greater than 500 years but can be
strongly influenced by environmental factors. By combining leaching
experiments and modeling, our results reveal that PVC microplastics
are a long-term source of phthalates in the environment.
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