Effect of seawater salinity on pore-size distribution on a poly(styrene)-based HP20 resin and its adsorption of diarrhetic shellfish toxins

• HP20 resin bags were deployed in three artificial seawaters at different salinity.
• Dynamic adsorption behavior of OA and DTX1 by these SPATT bags was explored.
• The highest initial sorption rate of toxins occurred in seawater at medium salinity.
• Resin pores below 10 nm in size governed adsorption in natural seawater.
• Toxins were retained by pores in seawaters at high and low salinity.

In the present study, okadaic acid (OA) and dinophysistoxin-1 (DTX1) were spiked into artificial seawater at low, medium and high estuarine salinities (9‰, 13.5‰ and 27‰). Passive samplers (HP20 resin) used for solid phase adsorption toxin tracking (SPATT) technology were exposed in these seawaters for 12-h periods. Adsorption curves well fitted a pseudo-secondary kinetics model. The highest initial sorption rates of both toxins occurred in the seawater of medium salinity, followed by seawater of low and high estuarine salinity. Pore volumes of micropores (<2 nm) and small mesopores (2 nm < diameter < 10 nm) of HP20 resin decreased after adsorption of toxins in seawater at high and low salinity but not in seawater at medium salinity, which demonstrated that the toxin molecules entered into micropores and mesopores (below 10 nm in size) in seawaters of high and low salinity. More toxin or other matrix agglomerates were displayed on the surface of resin deployed in the seawater of medium salinity. Taking into consideration the pore-size distribution and surface images, it appears that intra-particle diffusion governs toxin adsorption in seawater at high salinity while film diffusion mainly controls the adsorption process in seawater at medium salinity. This is the first study to confirm that molecules of OA and DTX1 are able to enter into micropores (<2 nm) and small mesopores (2–10 nm) of HP20 resin in estuarine seawater with high salinity (∼27‰).