Biomedical subjects

T C Feijtel

Publications and source records attributed to T C Feijtel.

5 recordsLinked to original sources

PubMed1998

A simplified modeling approach using microbial growth kinetics for predicting exposure concentrations of organic chemicals in treated wastewater effluents.

Various mathematical relationships have been used to assess exposure concentrations of organic chemicals when emissions occur via wastewater treatment. These relationships range from a simple removal factor calculation to more sophisticated approaches using kinetic based mathematical models. While these existing approaches have been used by decision makers to screen new chemicals for exposure assessments, they all have limitations in the predictive capabilities. Thus, a simplified modeling approach grounded in sound scientific fundamentals that utilizes relatively easy to obtain input parameters is needed. In this paper a simplified modeling approach that utilizes microbial growth kinetics was developed for predicting effluent concentrations in secondary biological wastewater treatment systems. Receiving water predicted exposure concentrations (PEC) are assessed by using a dilution factor. One advantage of this approach is that it allows for wastewater treatment plant effluent concentrations, and therefore receiving water exposure levels, to be predicted with a minimum amount of experimental data. It also provides quantitative data that can be used to assess the relative biodegradability of different chemicals for use in regulatory and risk assessment activities.

Bacteria↗

PubMed1997

The identification of thresholds of acceptability and danger: the chemical presence route.

European Union chemical legislation requires the calculation of local and regional Predicted Environmental Concentrations (PEC) for the assessment of the exposure of new and existing chemicals to aquatic and terrestrial ecosystems. Current methods use local models for air, water and soil to estimate chemical concentrations close to the source and a generic multimedia 'unit world' approach to estimate regional PECs. These models assume generic environmental scenarios representing typical situations in European countries and do not account for the spatial heterogeneity and temporal variability in ecosystem characteristics, soil properties, river flow rates, chemical emissions, etc. The environmental and ecological complexity can best be represented in a Geographic Information System (GIS). By coupling a GIS with a fate simulation model the concentrations of substances in a specific environment are predicted more realistically. The GREAT-ER project (Geography-referenced Regional Exposure Assessment Tool for European Rivers) was launched to refine regional and local exposure assessments for down-the-drain chemicals by applying real, spatial-referenced datasets instead of generic or average values. A modular approach was developed consisting of a hydrological model and a waste-flow, river quality and fate model which are linked to a regional GIS-database. For the calibration and validation in two European study areas representative detergent chemicals (LAS, boron) are used. In a parallel study, high-volume intermediates discharged into the river Rhine are simulated.

Alkanesulfonates↗

PubMed1997

Biodegradation of [S,S], [R,R] and mixed stereoisomers of ethylene diamine disuccinic acid (EDDS), a transition metal chelator.

An in-depth biodegradation test program was executed on the hexadentate ligand Ethylene Diamine Di Succinate (EDDS). The EDDS structure contains two chiral carbon atoms, and has three stereoisomers ([R,R], [R,S]/[S,R], [S,S]). Our research has focused on the isomer mixture (i.e. 25%[S,S]; 25%[R,R]; 50%[S,R]/[R,S], as produced from the reaction of ethylene diamine with maleic anhydride) and on the single [S,S]- and [R,R]-isomers. Biodegradation screening of the 14C-labelled EDDS isomer mixture in a Batch Activated Sludge (BAS) test with various inocula revealed incomplete mineralization, up to ca. 65% after 28 days. N-(2-aminoethyl) aspartic acid (AEAA), probably the d-isomer, was identified as the major portion of the 14C-material remaining in solution. Further testing revealed that the [S,S]-isomer is rapidly and completely mineralized in all test systems. By contrast, [R,R]-EDDS remained undegraded in a Sturm (OECD 301B) test, but was very slowly biotransformed into the recalcitrant metabolite AEAA in a BAS test. The [S,R]/[R,S] form undergoes biotransformation to AEAA in both high and low biomass systems. In a sewage treatment simulation test (OECD 303) the steady state DOC removal of mixture-EDDS in a CAS test was limited to 25-35%, even after extensive pre-acclimation, while the [S,S]-isomer achieved nearly complete removal (96%). This study illustrates the importance stereospecificity may have on the biodegradation and metabolite formation of a chemical. A biodegradation scheme for the different EDDS stereoisomers is proposed.

Aspartic Acid↗

PubMed1997

Seasonal temperature declines do not decrease periphytic surfactant biodegradation or increase algal species sensitivity.

The effects of seasonally decreasing river water temperature on surfactant biodegradation and algal sensitivity are reviewed from four stream mesocosm studies conducted over a 5-year period. Seasonal temperatures ranged from 28 to 0 degree C over all studies and temperature declines were approximately 9 to 14 degrees C over the course of each individual study. Mesocosm periphyton were naturally colonized on tile substrata with in-flowing river water for a period of 3 to 8 weeks prior to the initiation of sampling. Streams were dosed for 8 to 11 weeks with microgram/L (ppb) quantities of the surfactants C12-alkyl sulfate (C12-AS), C45E2.17S-alkyl ethoxysulfate (AES), C25E6-alkyl ethoxylate (AE) or 0 to 13% final effluent during the sampling period. Mineralization of C12-AS and AE by periphyton in the dosed streams generally increased over the dosing period while mineralization remained approximately constant in the control streams. The results from the AE study occurred with an increase in periphyton heterotrophic respiration. Mineralization of AES increased over the dosing period in streams receiving the highest dose of AES and remained constant in streams receiving lower doses. All studies involving surfactant exposure demonstrated a positive correlation between surfactant concentration and mineralization during periods of seasonal temperature decline. Mineralization of AE by periphyton dosed with final effluent increased slightly over the testing period. Periphytic algal taxonomy and biovolume were evaluated during the AES study. Overall, these tests showed no increases in species sensitivity over the testing period. Taken collectively, these results indicate that there is no correlation between naturally decreasing seasonal temperatures and lower rates of surfactant mineralization or increased species sensitivity by naturally acclimated periphyton.

Biodegradation, Environmental↗

PubMed1996

Impact of biodegradation test methods on the development and applicability of biodegradation QSARs.

The biodegradability of a substance depends on the structure and physical form of the substance, the time that has been available for acclimation, and the environmental conditions. Importantly, these later factors can be just as important as structure in determining the outcome of a biodegradation test. The development of appropriate QSARs for biodegradation and the ultimate value of the final QSAR depends on understanding these factors. This paper will describe what is known about the effect of test conditions on the results of biodegradation tests. The ability of these tests to reflect real environmental conditions will also be examined. Finally, we will discuss what we believe, in the light of this information, should be the goal of biodegradation QSARs and how these QSARs can be most appropriately used in fate assessments.

Bacteria↗