Synthetic organic compounds belonging to different chemical classes and possessing diverse physicochemical properties are frequently present in marine environments. Microplastics, pharmaceuticals, pesticides, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) are contained in the list of persistent organic pollutants (POPs) that have been detected in the global marine system. Numerous ecotoxicological studies have revealed the direct and indirect effects of anthropogenic toxicants on marine biota. The present review presents the research that has been conducted during the period from 1 January 2016 to 30 June 2021 concerning the lethal and sub-lethal impacts of selected organic-synthetic stressors on different plant and animal marine species, and summarizes the observed or predicted individual and combined effects after exposure to chemical mixtures of such contaminants. Future research needs dependent on the knowledge gaps that remain in the bibliography are also highlighted.

Laboratory studies were conducted to determine the sorption and desorption behaviour of two commonly used organophosphorus pesticides dimethoate and fenthion, which are widely used in the studied area to treat the olivetrees. Three Greek soils from the region of Mytilene island (denoted M, KT and P) which differed with respect to pH (pH 5.45–6.90), clay content (6–26%), organic matter content (1.0–4.2%), cation exchange capacity (4.8–24.4 meq/100 g) and specific surface (10.79–109.22 m² g⁻¹) were selected for the experimental section that was conducted using the batch equilibrium technique. The sorption isotherms could be described by Freundlich and Langmuir equations for both compounds with correlation regression coefficients for fit of the isotherms to that models R ² ≥ 0.9666 and R ² ≥ 0.8117, respectively. Freundlich sorption coefficients K_f were normalised to soil organic matter content and K_OM estimated values for M, KT and P soils respectively were 60.19, 163.58 and 663.43 for dimethoate and 1365.84, 820.73 and 2902.52 for fenthion. Desorption studies revealed that dimethoate was adsorbed very weakly on soils tested and easily desorbed with water, while on the contrary fenthion was adsorbed very strongly on studied matrices with acetone extractable amounts.

The photocatalytic degradation of five selected organophosphorus pesticides (OPPs), azinphos methyl, azinphos ethyl, disulfoton, dimethoate, and fenthion, has been investigated using TiO2 (photocatalyst) and UV irradiation. The addition of H2O2 (oxidant agent) into the illuminated aquatic suspensions was also surveyed. The degradation kinetics was studied under different experimental conditions such as pesticides’ and catalyst’s concentration. Experiments were performed in a Pyrex UV laboratory-constructed photoreactor equipped with 4 × 18 W low-pressure Hg lamps emitting at 365 nm (maximum intensity 14.5 mW cm−2 at distance 15 cm). The concentration of pesticides was determined by GC-NPD means. The extent of pesticide mineralization was assessed through TOC measurements. The results demonstrated that photolysis of target organophosphates in the absence of catalyst or oxidant is a slow process resulting in incomplete mineralization. Contradictory, studied pollutants were effectively degraded in the presence of TiO2; evolution of inorganic heteroatoms (SO42−, PO43−, NO2−, NO3−, and NH4+) as final products provided evidence that pesticide deterioration occurred. The photolysis efficiencies decreased in the order: disulfoton > azinphos ethyl > azinphos methyl > fenthion > dimethoate. Furthermore, a synergistic effect was observed with the addition of H2O2 in the pesticide-TiO2 suspensions. In all cases examined, reduction process appeared to follow pseudo first-order kinetics (Langmuir-Hinshelwood model). In conclusion, both catalytic systems investigated (UV-TiO2 and UV-TiO2-H2O2) have good potential for small-scale applications.

This chapter provides the results of a laboratory ecotoxicological study conducted to assess the acute toxicity of the organophosphorus pesticide fenthion toward the marine microalgal species Tetraselmis suecica. Bioassays were performed, and algal densities and chlorophyll pigments fractions were measured in the exponential phase after 96 h of exposure to fenthion. Two quantitative structure activity relationships (QSARs) were used to estimate the toxicity of 13 primary metabolites and degradation products of fenthion toward the selected organism; the first was based on the use of the n-octanol/water partition coefficient, whereas the second was based on the solubility of the compound in water. Results revealed that fenthion can have marked effects on the growth and photosynthesis of the target primary producers of marine ecosystems T. suecica. The parent pesticide toxicant was found not toxic to the tested algal species up to 1.00 mg L−1, while higher treatment concentrations not only affected algal densities and significantly decreased specific growth rate values (μ) (p < 0.05) but also decreased the contents of photosynthetic pigments. The comparison between the observed and the predicted toxicity values of the parent compound fenthion indicated that the predictive capability of the QSARs applied can be considered highly satisfactory. Consequently, both QSAR models were used for the prediction of toxicity data of fenthion’s principal metabolites and degradation products.

This study concerns the investigation of the sorption and desorption phenomena of the organic dye methylene blue (MB) on three different marine sediments and non-living biomass of the seagrass species Posidonia oceanica. All tested adsorbents were of natural origin and were collected from unpolluted coasts of the North Aegean Sea (Greece). The batch equilibrium technique was applied and MB concentrations were determined by spectrophotochemical analysis (λ = 665 nm). The experimental results showed that all four isotherm models, Freundlich, Langmuir, Henry, and Temkin, could describe the process. The normalized to organic matter content adsorption coefficients (K_OM) ranged between 33.0765 and 34.5279 for the studied sediments. The maximum adsorption capacity (q_max) of sediments was in the range of 0.98 mg g⁻¹ and 6.80 mg g⁻¹, indicating a positive correlation with the adsorbents’ organic matter content, textural analysis of fine fraction (<63 μm), and specific surface area. The bioadsorption of MB on P. oceanica biomass resulted in 13.25 mg g⁻¹ up to 17.86 mg g⁻¹ adsorption efficiency. Desorption studies revealed that the studied dye in most cases was very strongly adsorbed on studied matrices with extremely low quantities of seawater extractable amounts (≤1.62%). According to the experimental findings, phycoremediation by using P. oceanica can be characterized as an efficient method for the bioremediation of dye-polluted wastewater.