Modeling the differential functional responses and selectivity of a marine copepod to nano/microplastics in mixture.

Nano- and microplastics (NMPs) pollution is widespread in the oceans, posing potential risks to marine species. This study examined the accumulation capacity and selectivity potentials of NMPs by a marine copepod Parvocalanus crassirostris under different food mixtures by modeling the combined biokinetic and functional response. We investigated two sizes of NMPs (200 nm and 5 µm) across a concentration gradient (0 - 5000 µg/L) and varying diatom abundances (0, 104, 105 cells/mL). Fluorescence imaging and quantification revealed that P. crassirostris actively ingested NMPs at low concentration. Accumulation increased with NMPs concentration but eventually saturated due to gut capacity limits, following a Holling type II functional response (i.e., hyperbolic curve). Our novel functional response model estimated the key parameters and demonstrated that the maximum accumulation reached 5.3 % of dry weight with averaged half-saturation constants of 229 µg/L. The size of NMPs did not significantly affect the total accumulation or satiety levels. The presence of diatoms influenced the feeding selectivity and decreased the microplastic accumulation by 73 % at 105 cells/mL, while facilitating nanoplastic accumulation by 81 % at 104 cells/mL. This study enhanced our understanding of NMPs bioavailability and environmental fate in marine ecosystems.

Tracking Nano- and Microplastics Accumulation and Egestion in a Marine Copepod by Novel Fluorescent AIEgens: Kinetic Modeling of the Rhythm Behavior.

Nano- and microplastics (NMPs) are now prevalent in the marine environment. This study quantified the uptake and depuration kinetics of spherical polystyrene NMPs of different particle sizes (200 nm/30 µm) and functional groups (-NH2/-COOH) in a temperate calanoid copepod Calanus sinicus (C. sinicus), which exhibited rhythmic feeding patterns in natural environments. Aggregated-induced emission (AIE) fluorescent probes were employed to track and quantify the kinetics of NMPs with excellent photostability and biocompatibility. The results showed that C. sinicus consumed all NMPs types, with preference of NMPs to small size and amino group. Increased diatom concentrations also inhibited the bioaccumulation of NMPs. Influenced by rhythmic behavior, the bioaccumulation of NMPs by C. sinicus was nonstationary during the 6 h uptake phase. After 1-3 h of rapid uptake, the body burden peaked and then slowly declined. During the 3 h depuration phase, C. sinicus rapidly and efficiently removed NMPs with a mean half-life of only 0.23 h. To further quantify the body burden of C. sinicus under the influence of rhythmic feeding behavior, a biokinetic model was established, and the Markov chain Monte Carlo method was used to estimate the parameter distribution. Our results highlighted that copepods exhibited unique rhythmic feeding behavior under environmentally relevant concentrations of NMPs exposure, which may influence the bioaccumulation, trophic transfer, and environmental fate of NMPs.