Description of adsorption of hydrophobic organic compounds on sediment using multi-component adsorption model

A chemical sequential separation procedure for sediment has been developed for the adsorptive investigation of hydrophobic organic compounds(HOCs) including four fractions: carbonate, hydrous metallic oxide(ferric oxide, manganese oxide and alumina), clay and organic matter. Adsorption isotherms of these hydrophobic solute probes, such as hexachloroethane, lindane and 1,2,4,5 tetrachlorobenzene were measured for model sorbents, model and natural sediment, and the latter of which was pretreated with the simplified sequential separation method. The linear and Langmuir models are applied to correlate the experimental data of humic substance and other model sorbents respectively. Multi component Adsorptive Model (MCAM) was used to simulate adsorption isotherms of model and natural sediment. The results reveal that(1) the separation efficiencies of carbonate, organic matter, ferric oxide, manganese oxide and alumina are 98.1%, 72.5%, 82.6%, 93.5% and 83.3%, respectively; (2) except for removing metallic oxide, the external structure of sediment is not changed greatly after separation; (3) the MCAM correlates the data of adsorption isotherm rather well with the maximal relative deviations of 9.76%, 6.78% and 9.53% for hexachloroethane, lindane and 1,2,4,5 tetrachlorobenaze in model sediment, respectively. The MCAM can clearly give expression to the different adsorptive mechanisms for HOCs in organic and inorganic matter, though the experimental data in each component are not very accurate due to the sequential separation efficiency.

Bioaccumulation of toxic hydrophobic organic compounds at the primary trophic level

The prevailing hypothesis, which states that the uptake of HOCs by phytoplankton is controlled by the compound's lipophilicity (Kow) was tested. The approach taken was to determine the factors that controlled the uptake of PCBs by phytoplankton under controlled laboratory conditions, and to develop a model that would describe bioaccumulation of PCBs in phytoplankton.The results demonstrate a relationship of BAF to Kow and to phytoplankton surface properties, as well as the data presented here, support the hypothesis that the mechanism of HOC uptake is a rapid surface sorption followed by a slower transfer into lipids in the cell matrix. The work on the kinetics of uptake indicates that equilibrium is reached slowly and that the rate of uptake is of similar magnitude as phytoplankton growth under normal field conditions.Thus a critical factor that controls the bioaccumulation of HOCs reach equilibrium in phytoplankton itself.

Adsorptive removal of hydrophobic organic compounds by carbonaceous adsorbents:A comparative study of waste-polymer-based,coal-based activated carbon,and carbon nanotubes

Adsorption of the hydrophobic organic compounds （HOCs） trichloroethylene （TCE）, 1,3-dichlorobenzene （DCB）, 1,3-dirdtrobenzene （DNB） and y-hexachlorocyclohexane （HCH） on five different carbonaceous materials was compared. The adsorbents included three polymer-based activated carbons, one coal-based activated carbon （F400） and multiwalled carbon nanotubes （MWNT）. The polymer- based activated carbons were prepared using KOH activation from waste polymers： polyvinyl chloride （PVC）, polyethyleneterephthalate （PET） and tire rubber （TR）. Compared with F400 and MWNT, activated carbons derived from PVC and PET exhibited fast adsorption kinetics and high adsorption capacity toward the HOCs, attributed to their extremely large hydrophobic surface area （2700 m2/g） and highly mesoporous structures. Adsorption of small-sized TCE was stronger on the tire-rubber-based carbon and F400 resulting from the pore-filling effect. In contrast, due to the molecular sieving effect, their adsorption on HCH was lower. MWNT exhibited the lowest adsorption capacity toward HOCs because of its low surface area and characteristic of aggregating in aqueous solution.

Relationship between metabolic enzyme activities and bioaccumulation kinetics of PAHs in zebrafish(Danio rerio)

Many studies have investigated bioaccumulation and metabolism of polycyclic aromatic hydrocarbons（PAHs）in aquatic organisms.However,lack of studies investigated both processes simultaneously,and the interaction between these two processes is less understood so far.This study investigated the bioaccumulation kinetics of PAHs and metabolic enzyme activities,including total cytochrome P450（CYPs）and total superoxide dismutase（T-SOD）,in zebrafish.Mature zebrafish were exposed to the mixture of phenanthrene and anthracene under constant concentration maintained by passive dosing systems for 16 days.The results showed that PAH concentrations in zebrafish experienced a peak value after exposure for 1.5 days,and then decreased gradually.The bioaccumulation equilibrium was achieved after exposure for 12 days.Both of the uptake rate constants（ku）and the elimination rate constants（ke）decreased after the peak value.The variation of PAH concentrations and metabolic enzyme activities in zebrafish had an interactive relationship.The activities of CYPs and T-SOD increased initially with the increase of PAH concentrations,but decreased to the lowest state when PAH concentrations reached the peak value.When the bioaccumulation equilibrium of PAHs was achieved,CYPs and T-SOD activities also reached the steady state.In general,CYPs and T-SOD activities were activated after exposure to PAHs.The decrease of PAH concentrations in zebrafish after the peak value may be attributed to the great drop of kuand the variation of CYPs activities.This study suggests that an interactive relationship exists between bioaccumulation kinetics of PAHs and metabolic enzyme activities in aquatic organisms.