New spectroscopic method for true color determination in natural water with high agreement with visual methods.

True water color (TWC) is an important water quality indicator. However, despite many efforts for standardization of methods for TWC determination, there is still no consistency between visual and spectroscopic techniques. This study demonstrates that standard spectroscopic methods overestimate visual data from 21 to 47%, depending on methods involved. To retrieve relevant true water color values from spectral data, a new spectroscopic method is proposed. The method is based on the mathematical model of color perception by the standard observer implementing the dE2000 color difference in the L∗a∗b color space as calculated between blank and water samples. The method showed good agreement with the visual methods (comparator method and determination in Nessler cylinders) and the mean values between these methods. The mean relative difference between the proposed method and the mean of the two visual methods is only 2%. The method precision is independent from TWC in all measurement ranges and has Sr 0.3 mgPt-Co L-1 (df = 98), which is at least three times lower than for the standard methods. As such, it shows higher accuracy and precision. As a result, the proposed method can be used for TWC determination in environmental samples from 3.3 to 500 mgPt-Co L-1 with SD 0.3 mgPt-Co L-1 in all measuring ranges, making sample dilution unnecessary.

Microplastic content variation in water column: The observations employing a novel sampling tool in stratified Baltic Sea.

A new tool was developed for microplastics (MPs) investigation in the water column. It can collect several cubic meters of water from predefined water layers down to 100 m. The tool was tested in the Baltic Sea during the period of spring thermocline formation. Strong MPs stratification was observed at all of the sampled stations. On coastal stations (~30 m deep), stratification with high fibers content was associated with the proximity of terrestrial sources and estuarine discharges, while on off-shore stations the variability of MPs was related to vertical thermohaline structure. Mean MPs content was the 32.2 (SD 50.4) pcs/m3. Elevated MPs concentrations were observed in subsurface, near-bottom and thermohaline layers compared with intermediate layers. The heterogeneity of MPs distribution suggests that MPs particles can be retained above the density-gradient layers in coastal seas and the World Ocean.