Contaminant uptake

For the estimation of the contaminants uptake rate and consequently the time required for the phytoremediation of a contaminated site, single mathematical models may be applied. In the following paragraphs, analysis as well as the examples given in Groundwater Remediation Technologies Analysis Center Technology Evaluation Report on Phytoremediation, by Schnoor, is presented without modification.8... 

In order to properly interpret differences in sampling rates among compounds and among exposure conditions, it is important to discriminate between membrane-controlled uptake and WBL-controlled uptake. From Eq. 3.8 (in the absence of biofouling), contaminant uptake is rate-limited by the membrane when... 

Booij et al. (2003b) made an effort to model contaminant uptake by buried passive samplers. The major assumptions underlying this model are that the sampler can be regarded as an infinite sink for target contaminants, that the depletion of the bulk sediment phase is insignificant, and that the contaminant desorption kinetics are not rate-limiting. 

Figure 7.1 Comparison of the patterns of organic contaminant uptake rates (as related to log Kows) by SPMDs and across fish gills (McKim et ah, 1985). Reprinted with permission from the American Petroleum Institute (Huckins et al., 2002).

Peven, C.S. Uhler, A.D. Querzoli, FJ. 1996, Caged mussels and semipermeable membrane devices as indicators of organic contaminant uptake in Dorchester and Duxbury Bays, Massachusetts. Environ. Toxicol. Chem. 15 144-149. 

Rogers, H.R. 1997, Influence of suspended sohds and back diffusion on organic contaminant uptake by semi-permeable membranes (SPMDs). Chemosphere 35 1651—1658. 

Our results show how radiophytoremediation can be applied to a practical situation, at least in the case of waste-water treatment, where the pattern of contaminant uptake is likely to resemble that observed in hydroponics experiments. For soil-cleaning purposes, the solubility of the... 

Indirectly improves nearby water quality through nutrient and contaminant uptake. 

Brisbin et al. (30) described the development of the Richards sigmoidal model and presented it as an equation for contaminant uptake based on the amount of contaminant in an organism or compartment. For our data, the equation was reparameterized to use a partition coefficient rather than a concentration. It takes the form... 

The dose or contaminant body residue in organisms is a key determinant of potential risk from contaminant uptake. For instance, metal body concentrations in small exposed organisms can be related to metal-induced effects at the organism and population levels of organization (Chapman et al., 2003). CBRs have been used, similar to TIEs, to establish causation as part of the SQT (Borgmann et al., 2001), and to provide additional information for predictions related to changes in contaminant loadings. 

Several studies have focused on clarifying the pathways of contaminant uptake.17,74-76 These will depend not only on the specific aspects of a contaminant, but will also be species-specific and influenced by environmental variables interpretational difficulties will inevitably ensue. For this reason, laboratory assays under controlled conditions are commonly used to assess the relative importance of each pathway in the overall contaminant accumulation in aquatic biota, and also the effect of altering environmental variables. Such studies can prove to be useful tools not only when... 

Sediment contact tests are biological methods for the determination of toxic effects induced by whole sediments in direct contact with test organisms, taking into account all possible pathways of contaminant uptake (particle contact, food, pore water). Sediment contact tests are highly relevant in order for an ecosystem approach to consider the actual bioavailability of contaminants sufficiently. 

Uptake rates may also differ with age. Young children, for example, absorb lead via the gastro-intestinal tract four to five times more efficiently than adults, which makes them more susceptible to the effects of lead. Certainly much work remains to be done on soil contaminant uptake rates but current research illustrates that uptake rates are highly variable and dependent on a range of factors such as the contaminant type, physical and chemical properties of the soil, residence time in the gut etc. 

Exposure assessment involves modelling, as appropriate and relevant, contaminant uptake via ingestion, inhalation and skin contact routes. At its simplest, risk assessment, therefore, consists of comparing total daily uptake (i.e. from both soil and background sources) with a tolerable daily uptake as advised by authoritative toxicologists. 

Ferguson and Marsh25 describe the basis for contaminant uptake through soil ingestion. 

Yin, C. Y M.K. Aroua, and W.M.A.W. Baud, Review of modifications of activated carbon for enhancing contaminant uptakes from aqueous solutions Separation and Purification Technol. 2007, 52(3), 403-415. 

Yin, C. Y., M. K. Aroua, and W. M. A. W. Daud, Review of Modifications of Activated Carbon for Enhancing Contaminant Uptakes from Aqueous Solution, Separation Purification Techniques, 52, 403-415 (2007). 

In aquatic sediments or soils, there are also a range of trace elements species ranging from ions exchanged to particles, to those bound to organic matter or in various inorganic forms (e.g., oxides, carbonates, sulfides) or as more inert crystalline mineral phases. As in waters, speciation studies in soils and sediments are generally undertaken to better understand the bioavailability of toxic substances and to investigate transport pathways to and from other parts of the ecosystem. Sediment and soil pore waters (soil solutions) are of particular interest because they are in equilibrium with the solid phase and are the medium for contaminant uptake by plants and many other biota. The techniques used for speciation analysis in these aqueous samples differ little from those for waters. 

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