Hydrophobic organic contaminants toxicity

Crystalline salts of many organic acids and bases often have a maximum solubility in a mixture of water and water-miscible solvents. The ionic part of snch a molecule requires a strongly polar solvent, snch as water, to initiate dissociation. A mixture of water-miscible solvents hydrates and dissociates the ionic fraction of pollutants at a higher concentration than wonld either solvent alone. Therefore, from a practical point of view, the deliberate nse of a water-soluble solvent as a cosolvent in the formnlation of toxic organic chemicals can lead to an increased solnbility of hydrophobic organic contaminants in the aqueous phase and, conse-qnently, to a potential increase in their transport from land surface to groundwater. 

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

Hydrophobic organic contaminants, such as PAHs, are a large group of persistent and toxic contaminants in the subsurface. They repel water, and thus have low water... 

McCarthy JF (1989) Bioavailability and toxicity of metals and hydrophobic organic contaminants. In Suffet IH, MacCarthy P (eds) Aquatic Humic Substances Influence on Fate and Treatment of Pollutants. Advances in Chemistry Series 219. American Chemical Society, Washington, DC, pp 263-277. 

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic pollutants (POPs) and widespread environmental contaminants, some of which may exhibit toxic, carcinogenic and mutagenic effects Because of their low water solubility and hydrophobic nature, PAHs are partitioned... 

Humic and FULVIC acids, along with other organic colloidal materials, are fascinating substances that can have profound environmental consequences. Their abilities to complex radionuclides and toxic metals have been recognized for some time by researchers interested in the migration and mobilization of nuclear and industrial waste at contaminated sites. The micellar properties of humic and fulvic acids also give them the ability to play important roles in the solubilization and transport of hydrophobic pollutants. 

In addition to direct membrane analogs, many researchers have used Cg, Cis, and XAD resins to simulate the bioavailability of organic compounds. Lake et al. (1996) used Cig resins as a surrogate for benthic organism bioaccumulation of hydrophobic compounds from sediments. Gustafson and Dickhut (1997) and Ankley et al. (1991) also utilized resins to sorb compounds for the assessment of toxicity (and bioavailability) of contaminants in sediments. 

Physiologically based toxicokinetic (PB-TK) models are used to describe the kinetics of uptake and depuration of hydrophobic contaminants by an organism. The great promise of PB-TK models lies in their potential to link contaminant concentrations in specific tissues with toxic effects in those tissues. We will discuss these models only in relation to the premise that lipid class significantly affects the kinetics of lipophilic chemical uptake and release. For in-depth descriptions of PB-TK models in fish, several excellent reviews and recent articles are available36,75,84,85. 

As microplastics move through the environment they can sorb and transport other contaminants. Plastic debris scooped from the ocean has contained polychlorinated biphenyls (PCBs) at concentrations up to 5 parts per million and dichlorodiphenyltrichloroethane (DDT) at approximately 7 PPM, for example [145-147]. Of particular concern are persistent, bioac-cumulative, and toxic (PBT) compounds that would tend to partition into a plastic matrix due to their hydrophobicity the logical inference is fhaf floaf-ing microplastics could transport PBT compounds through the environment and that perhaps the PBT compounds would enter the food chain as organisms ingested fhe plastic fragments. 

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