Effects of synthetic zeolite “A” and polycarboxylates on quality and quantity of diatom mucous exudates

With the objective to understand whether the introduction on the market of phosphorus-free detergents, namely of detergents based on Zeolite A and Poly Carboxylic Acid (PCA) as builder system, may have played a role in the development of the mucilage phenomenon in the Northern Adriatic Sea (Italy), a experimental study has been undertaken in laboratory. Using diatomCylindrotheca closterium (Ehr.) Reimann and Lewin as inoculum, which is considered as the most important microalgal organism responsible for mucilage production, several tests have been carried out, adding the Zeolite A and PCA system, at various concentrations, fractions and ratios, to aged filtered seawater. Under controlled conditions the mucous aggregates formation has been followed and photographed, collecting and then measuring their volumes and dry weights, and at last calculating density, porosity and excess of density. Statistical analysis applied to all collected data has revealed an homogenous response of this microalgal species and comparable parameters for the mucous aggregates both in the blank and in the tests with Zeolite A and PCA. Our experimental study has not revealed any evident causal relationship between the presence of Zeolite A — PCA system and the formation of mucous aggregates.