POPs are a group of chemicals that have been extensively studied over the last few
years. The main reason that these chemicals have received so much scientific
attention is the myriad of negative effects they have on the environment and human
health. The properties that cause the deleterious effects include a high molecular
stability, rendering them highly persistent. Added to this is the lipophilic and
hydrophobic nature of the compounds. POPs will thus tend to bio-accumulate and
bio-magnify in the environment, causing a direct threat to humans and wildlife. To
address this threat, the Stockholm Convention on Persistent Organic Pollutants,
under the supervision of United Nations Environment programme (UNEP), was
initiated and became legally binding on 17 May 2004. All countries, including South
Africa, which ratified this agreement, will be expected to monitor and regulate the
formation of POPs.
Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs)
and polychlorinated biphenyls (PCBs) are all members of the dioxin-like family of
POPs. This family of chemicals pose serious health threats such as carcinogenic
effects and negative effects on reproduction. These substances, with the exception of
PCBs, are formed unintentionally as by-products of industrial and thermal processes.
One of the main sources of dioxin-like chemicals is medical waste incinerators.
In this project the area surrounding a medical waste incinerator was monitored using
a bio-assay technique. The determination of dioxin concentrations is usually
preformed by chemical analysis, however, bio-assays have proven themselves to be
a cheaper and time-saving screening method. The Toxic Equivalency Quotient
(TEQs) determined through bio-assays can support chemical analysis in determining
biologically-relevant risk assessments since bio-assay data has ecotoxicological
relevance. These assays represent an integrated biological response to chemical
pollutants, where biological effects are accounted for which is not possible in
chemical analyses. One of the bio-assays used in the determination of the dioxin-like
chemical TEQ is the H411 E reporter gene bio-assay. This assay is based on the Ah-receptor
mediated toxicity of dioxin-like chemicals. Using this technique the TEQs for
areas surrounding an active incinerator were determined, to indicate the distribution
of these substances. The TEQs for the soil samples collected ranged between nondetectable
and 154 ngTEQ/kg. There was no clear distributional pattern and the total
organic carbon content in the soil did not seem to play a crucial role in the distribution
of dioxin-like chemicals. Although a decrease in soil tillage showed a corresponding
increase in TEQ. The predominant wind direction was taken into account but no
correlation could be seen. However, meteorological parameters such as the ambient
temperature and low precipitation in the area may have contributed to lower TEQ
values. Cytotoxicity excluded data points and the phenomenon has to be addressed.
High TEQ values in a residential area where free-range chickens are raised pose a
serious concern to the level of dietary dioxin-like chemical intake. Eggs in the area
could theoretically contain between 2.75 and 28.75 pgTEQ/g egg fat. Further studies
are needed to determine how much dioxin-like chemicals are being transferred to
humans through the consumption of free-range eggs / Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2006.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/1013 |
| Date | January 2005 |
| Creators | Quinn, Laura Penelope |
| Publisher | North-West University |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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