Pelagic Sargassum spp. blooms pose a complex challenge to the Caribbean coast, affecting ecological, economic, and social dimensions. Since the formation of the Great Atlantic Sargassum Belt in 2011, these blooms have become an annual occurrence, lasting up to nine months each year. The Sargassum that washes ashore in the Western and Central Caribbean can reach tens of thousands of cubic meters per kilometer annually. These algae can carry pollutants, pathogens, and exotic species to coastal zones. As the algae decay, toxic gases and leachates are released, posing significant health risks to humans and other species. Ecologically, Sargassum landings contribute to beach erosion, nearshore waters eutrophication and transition from sandy to muddy sediments, and oxygen depletion, leading to losses in seagrass meadows flora and fauna. Mangrove ecosystems, inlets, and bays face disruptions in their biochemistry, hydrodynamics, and ecology, potentially shifting from carbon sinks to sources of greenhouse gases. Economically, the impact is severe, threatening the tourism and fishing industries crucial to the affected countries' economies. Socially, the blooms affect various aspects of well-being, including health, job quality, and connections to nature. Although progress has been made in understanding the impacts of Sargassum, much of the research has been concentrated in Mexico, primarily focusing on the ecological effects on coastal and beach environments. However, considerable knowledge gaps remain regarding the impacts of Sargassum on the ecosystems, economies, and social well-being of many other countries and territories in the region.

Emerging pollutants such as pharmaceuticals have been focusing international attention for a few decades. Ciprofloxacin (CIP) is a common drug that is widely found in hospital and wastewater treatment plants effluents, as well as in rivers. In this work, the feasibility of CIP degradation by ultrasound process at high frequency is discussed and sonolysis, sonolysis with hydrogen peroxide and sono-Fenton are evaluated. The amounts of hydrogen peroxide and ferrous ions (Fe²⁺) needed were optimized using response surface methodology. Best results were obtained with the sono-Fenton process resulting in a total pharmaceutical degradation within 15 min and a mineralization greater than 60% after 1 h. Optimal conditions were tested on a real matrix from a municipal wastewater treatment plant. Even if the degradation of the pollutants by sono-Fenton was hampered, the removal efficiency of both CIP and total organic carbon (TOC) is interesting as an increase in the biodegradability of the wastewater is found. These results show that sono-Fenton oxidation can be a promising pretreatment process for pharmaceutical-containing wastewaters.

Adsorption is one of the most successful physicochemical approaches for removing heavy metal contaminants from polluted water. The use of residual biomass for the production of adsorbents has attracted a lot of attention due to its cheap price and environmentally friendly approach. The transformation of Sargassum—an invasive brown macroalga—into activated carbon (AC) via phosphoric acid thermochemical activation was explored in an effort to increase the value of Sargassum seaweed biomass. Several techniques (nitrogen adsorption, pH_PZC, Boehm titration, FTIR and XPS) were used to characterize the physicochemical properties of the activated carbons. The SAC600 3/1 was predominantly microporous and mesoporous (39.6% and 60.4%, respectively) and revealed a high specific surface area (1695 m²·g⁻¹). To serve as a comparison element, a commercial reference activated carbon with a large specific surface area (1900 m²·g⁻¹) was also investigated. The influence of several parameters on the adsorption capacity of AC was studied: solution pH, solution temperature, contact time and Cr(VI) concentration. The best adsorption capacities were found at very acid (pH 2) solution pH and at lower temperatures. The adsorption kinetics of SAC600 3/1 fitted well a pseudo-second-order type 1 model and the adsorption isotherm was better described by a Jovanovic-Freundlich isotherm model. Molecular dynamics (MD) simulations confirmed the experimental results and determined that hydroxyl and carboxylate groups are the most influential functional groups in the adsorption process of chromium anions. MD simulations also showed that the addition of MgCl₂ to the activated carbon surface before adsorption experiments, slightly increases the adsorption of HCrO₄⁻ and CrO₄²⁻ anions. Finally, this theoretical study was experimentally validated obtaining an increase of 5.6% in chromium uptake.

Intensive use of chlorinated pesticides from the 1960s to the 1990s has resulted in a diffuse contamination of soils and surface waters in the banana-producing areas of the French West Indies. The purpose of this research was, for the first time, to examine the degradation of two of these persistent pollutants – chlordecone (CLD) and beta-hexachlorocyclohexane (β-HCH) in 1 mg L⁻¹ synthetic aqueous solutions by means of photolysis, (photo-) Fenton oxidation and ozonation processes. Fenton oxidation is not efficient for CLD and yields less than 15% reduction of β-HCH concentration in 5 h. Conversely, both molecules can be quantitatively converted under UV-Vis irradiation reaching 100% of degradation in 5 h, while combination with hydrogen peroxide and ferrous iron does not show any significant improvement except in high wavelength range (>280 nm). Ozonation exhibits comparable but lower degradation rates than UV processes. Preliminary identification of degradation products indicated that hydrochlordecone was formed during photo-Fenton oxidation of CLD, while for β-HCH the major product peak exhibited C₃H₃Cl₂ as most abundant fragment.