PMC:2854002 / 13996-16417
Annnotations
{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/2854002","sourcedb":"PMC","sourceid":"2854002","source_url":"https://www.ncbi.nlm.nih.gov/pmc/2854002","text":"Figure 1a clearly illustrates that free aqueous PCB concentrations estimated on the basis of KOW values, sediment TOC, and solid phase concentration according to eq 1 exceed actual measurements. This is true for all sediments, even those from relatively rural locations such as Lake Hartwell and Grasse River that did not have major industrial inputs other than PCB releases. The median overestimation is a factor of 8 and ranges from 2 for Grasse River (lowest BC/TOC ratio of 0.07) sediment to 17 for Niagara River (highest BC/TOC ratio of 0.31) sediment. It appears sorption by amorphous organic carbon (AOC) alone (as expressed by sediment TOC) is not sufficient to explain the PCB sorption displayed by any of these sediments, in accordance with similar previous observations (3,23). Figure 1b compares measured free aqueous PCB concentrations and those estimated using eqs 5 and 6, which are based on the solid phase concentration, KOW values, and sediment TOC but additionally account for adsorption to BC. The agreement between estimated and measured concentrations is improved; in agreement with previous observations (24−26), and here this is especially evident at free aqueous concentrations greater than 30 ng/L. Yet, it is notable that eqs 5 and 6 underestimate measured free aqueous concentrations in the lower concentrations range of approximately less than 30 ng/L. This is reflected in the statistics reported in Table 2. The median ratio of estimated to measured free aqueous PCB concentrations shows an underestimation of a factor of 4 when eqs 5 and 6 are used, compared to a median overestimation of a factor of 8 for the TOC based relationship. The Pearson’s correlation coefficient used to test the linearity of the relationship between estimated and measured data is also slightly improved from 0.90 to 0.93 when TOC is split to AOC and BC. Still, the fitted slope of the data in Figure 1b is higher than the theoretical value of 1 because of the systematic underestimation of free aqueous PCB concentrations below 30 ng/L. The HP sediment data have been included in the statistical analysis, despite the slower kinetics discussed above, as data points generally fall within the range of data for the other, finer sediments indicating that the PCBs in HP sediment are also close to sorption equilibrium. Statistics without the HP data set show the same overall trends and are provided in Table S1.","tracks":[{"project":"MyTest","denotations":[{"id":"19961220-15667088-28495512","span":{"begin":782,"end":783},"obj":"15667088"},{"id":"19961220-11811485-28495513","span":{"begin":1128,"end":1130},"obj":"11811485"}],"namespaces":[{"prefix":"_base","uri":"https://www.uniprot.org/uniprot/testbase"},{"prefix":"UniProtKB","uri":"https://www.uniprot.org/uniprot/"},{"prefix":"uniprot","uri":"https://www.uniprot.org/uniprotkb/"}],"attributes":[{"subj":"19961220-15667088-28495512","pred":"source","obj":"MyTest"},{"subj":"19961220-11811485-28495513","pred":"source","obj":"MyTest"}]},{"project":"2_test","denotations":[{"id":"19961220-15667088-28495512","span":{"begin":782,"end":783},"obj":"15667088"},{"id":"19961220-11811485-28495513","span":{"begin":1128,"end":1130},"obj":"11811485"}],"attributes":[{"subj":"19961220-15667088-28495512","pred":"source","obj":"2_test"},{"subj":"19961220-11811485-28495513","pred":"source","obj":"2_test"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"MyTest","color":"#a7ec93","default":true},{"id":"2_test","color":"#ec93c1"}]}]}}