Study of ceramic membrane behavior for okadaic acid and heavy-metal determination in filtered seawater

The performance of several MF and UF ceramic membranes that filter the seawater surrounding mussel rafts is studied for preventive detection of toxic episodes. The modified fouling index applied to UF membranes (MFI-UF) is used to compare fouling rates and membrane fouling levels. The reduction of several quality parameters such as turbidity, alkalinity, chemical oxygen demand (COD), and chlorophyll content is explained by the higher quality of the UF rather than the MF permeates. Membrane rejection rates of Pb⁺² and okadaic acid, the main toxin that provokes toxic episodes due to bloom-forming algae, are measured under different pH and pressures. Measurements are taken particularly at filtration times before and after the formation of stable caking on the membrane surface. The results indicated that trace concentrations of heavy ions were mainly rejected by the membrane charge, until the saturation point was reached, and that no rejections occurred when the pH was lower than the isoelectric point of the membranes. However, most of the okadaic acid was rejected due to the formation of cake on the membrane surface. The rejection of okadaic acid depended on the membrane pore size and transmembrane pressure, yielding negative rejections under specific filtration conditions.

Comparison of backing materials of screen printed electrochemical sensors for direct determination of the sub-nanomolar concentration of lead in seawater

An anodic stripping voltammetric method is reported in this study for the determination of sub-nanomolar Pb concentration using disposable sensors, each consisting of three (counter, working and reference) screen-printed electrodes. Sensor performance was optimized for the determination of Pb through several surface modifications, by using single-walled carbon nanotubes, electro-reduced graphene oxide and gold nanoparticles. A scanning electron microscopy study of the deposition of electrogenerated gold nanoparticles of various sizes on the working electrode surface showed that spherical nanoparticles of around 100 nm provided the best results. The modification of working electrodes with graphene and gold nanoparticles permitted the determination of Pb²⁺ in seawater (Detection Limit: 3.21·10^-10 M) without modifying the pH of the sample. The electrode systems were printed on both rigid and textile backing materials, to observe the influence of those materials on the final performance of the sensor.