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Unresolved complex mixture
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<h2 id="weathering-and-biodegradion-of-oils-within-the-marine-environment">Weathering and biodegradion of oils within the marine environment</h2> <p>Environmental UCMs result from highly degraded petroleum hydrocarbons and once formed they can stay largely unchanged in sediments for many years. For example, in 1969 a diesel <a href="/facts/Oil_spill/A1KGmKI6">oil spill</a> contaminated saltmarsh sediment within Wild Harbor River, US; by 1973 only a baseline hump was observed, which remained largely unchanged within the anaerobic sediment for the next 30 years.<a class="footnote-ref" id="fnref:46" href="#fn:46"><sup>46</sup></a> In a study of the potential for UCM-dominated oil to be further degraded, it was concluded that even using bacteria specifically adapted for complex UCM hydrocarbons in conjunction with nutrient enrichment, biodegradation rates would still be relatively slow.<a class="footnote-ref" id="fnref:47" href="#fn:47"><sup>47</sup></a> Bacterial degradation of hydrocarbons is complex and will depend on environmental conditions (e.g. aerobic or anaerobic, temperature, nutrient availability, available species of bacteria etc.). </p> <h2 id="analysis-of-ucm-hydrocarbons">Analysis of UCM hydrocarbons</h2> <p>A relatively recent analytical tool that has been used for the separation of UCMs is comprehensive two-dimensional GC (<a href="/facts/GCxGC/EmKV5VqN">GCxGC</a>). This powerful technique, introduced by Liu and Phillips<a class="footnote-ref" id="fnref:48" href="#fn:48"><sup>48</sup></a> combines two GC columns with different separation mechanisms: typically a primary column that separates compounds based on volatility coupled to a second short column that separates by polarity. The two columns are connected by a modulator, a device that traps, focuses and re-injects the peaks that elute from the first column into the second column. Each peak eluting from the first column (which may be a number of co-eluting peaks) is further separated on the second column. The second separation is rapid, allowing the introduction of subsequent fractions from the first column without mutual interference. Dallüge et al.<a class="footnote-ref" id="fnref:49" href="#fn:49"><sup>49</sup></a> reviewed the principles, advantages and main characteristics of this technique. One of the main advantages is the very high separation power, making the technique ideal for unravelling the composition of complex mixtures. Another important feature of GC×GC is that chemically related compounds show up as ordered structures within the chromatograms, i.e. isomers appear as distinct groups in the chromatogram as a result of their similar interaction with the second dimension column phase.<a class="footnote-ref" id="fnref:50" href="#fn:50"><sup>50</sup></a> The use of GC×GC for the characterization of complex petrochemical mixtures has been extensively reviewed.<a class="footnote-ref" id="fnref:51" href="#fn:51"><sup>51</sup></a> Most research into petrochemical hydrocarbons using GC×GC has utilised <a href="/facts/Flame_ionization_detector/XAJuoHTu">flame ionisation detection</a> (FID) but <a href="/facts/Mass_spectrometry/RH5WBHJ2">mass spectrometry</a> (MS) is necessary to obtain the structural information necessary to identify unknown compounds. Currently, only <a href="/facts/Time-of-flight_mass_spectrometry/6bj9bgGF">time-of-flight MS</a> (ToF-MS) can deliver the high acquisition rates required to analyse GC×GC. </p> <h2 id="toxicity-of-ucm-hydrocarbon-components">Toxicity of UCM hydrocarbon components</h2> <p>There is compelling evidence that components within some UCMs are <a href="/facts/Aquatic_toxicity/4aRsBDS7">toxic to marine organisms</a>. The <a href="/facts/Clearance_rate/xpzu5XIA">clearance rate</a> (also known as feeding feed) of <a href="/facts/Mussel/SNdrkjfl">mussels</a> was reduced by 40% following exposure to a monoaromatic UCM derived from a Norwegian crude oil.<a class="footnote-ref" id="fnref:52" href="#fn:52"><sup>52</sup></a> The toxicity of monoaromatic UCM components was further evidenced by an elegant set of experiments using transplantations of clean and polluted mussels.<a class="footnote-ref" id="fnref:53" href="#fn:53"><sup>53</sup></a> Recent analysis by GC×GC-ToF-MS of UCMs extracted from the mussel tissues, has shown that they contain a vast array of both known and unknown compounds.<a class="footnote-ref" id="fnref:54" href="#fn:54"><sup>54</sup></a> The comparative analysis of UCMs extracted from mussels known to possess high, moderate and low Scope for Growth (SfG), a measure of the capacity for growth and reproduction,<a class="footnote-ref" id="fnref:55" href="#fn:55"><sup>55</sup></a> revealed that branched alkylbenzenes represented the largest structural class within the UCM of mussels with low SfG; also, branched <a href="/facts/Isomer/PXlvDVdg">isomers</a> of alkyl<a href="/facts/Tetralin/0YFvrDQq">tetralins</a>, alkyl<a href="/facts/Indane/x6xKFHwh">indanes</a> and alkyl<a href="/facts/Indene/ENoRaBy8">indenes</a> were prominent in the stressed mussels.<a class="footnote-ref" id="fnref:56" href="#fn:56"><sup>56</sup></a> Laboratory toxicity tests using both commercially available and specially synthesised compounds revealed that such branched alkylated structures were capable of producing the observed poor health of the mussels.<a class="footnote-ref" id="fnref:57" href="#fn:57"><sup>57</sup></a><a class="footnote-ref" id="fnref:58" href="#fn:58"><sup>58</sup></a> The reversible effects observed in mussels following exposure to the UCM hydrocarbons identified to date are consistent with non-specific narcosis (also known as baseline) mode of action of toxicity.<a class="footnote-ref" id="fnref:59" href="#fn:59"><sup>59</sup></a> There is no evidence that toxic UCM components can <a href="/facts/Biomagnify/Jw5whhaj">biomagnify</a> through the <a href="/facts/Food_chain/mvDKQTGu">food chain</a>. Crabs (<i><a href="/facts/Carcinus_maenas/va5ldC57">Carcinus maenas</a></i>) that were fed a diet of mussels contaminated with environmentally realistic concentrations of branched alkylbenzenes, suffered behavioural disruption but only a small concentration of the compounds were retained in the midgut of the crabs.<a class="footnote-ref" id="fnref:60" href="#fn:60"><sup>60</sup></a> Within marsh sediments still contaminated with high concentrations of UCM hydrocarbons from the Florida barge oil spill in 1969 (see above,) the behaviour and feeding of fiddler crabs (<a href="/facts/Uca_pugnax/kgjbaCdQ">Uca pugnax</a>) was reported to be affected.<a class="footnote-ref" id="fnref:61" href="#fn:61"><sup>61</sup></a> </p> <h2 id="polar-ucms">Polar UCMs</h2> <p>Much of the past research into the composition and toxicity of UCM hydrocarbons has been conducted by the Petroleum and Environmental Geochemistry Group (PEGG)<a class="footnote-ref" id="fnref:62" href="#fn:62"><sup>62</sup></a> at the University of Plymouth, UK. As well as the hydrocarbon UCM, oils also contain more <a href="/facts/Polar_compound/KlIJ0zjB">polar compounds</a> such as those containing oxygen, sulphur or nitrogen. These compounds can be very <a href="/facts/Water_solubility/eRNr3MH2">soluble in water</a> and hence <a href="/facts/Bioavailable/9l6na9MV">bioavailable</a> to marine and aquatic organisms. Polar UCMs are present within produced waters from <a href="/facts/Oil_rig/lF82CEsg">oil rigs</a> and from <a href="/facts/Oil_sand/ewYn43lb">oil sands</a> processing. A polar UCM fraction extracted from North Sea oil produced water was reported to elicit <a href="/facts/Endocrine_disruptor/Yk2hfnTj">hormonal disruption</a> by way of both <a href="/facts/Estrogen_receptor/dEGaNney">estrogen receptor</a> agonist and <a href="/facts/Androgen_receptor/NBPRszqm">androgen receptor</a> agonist activity.<a class="footnote-ref" id="fnref:63" href="#fn:63"><sup>63</sup></a> Ongoing concern regarding the potential toxicity of components within <a href="/facts/Athabasca_oil_sands/oGj4xxtn">Athabasca Oil Sands</a> (Canada) tailings ponds has highlighted the need for identification of the compounds present. Until recently, such positive identification of individual so-called <a href="/facts/Naphthenic_acid/6QbBpU0q">naphthenic acids</a> from oil sands produced waters had so far eluded characterisation but recent research by PEGG presented at a <a href="/facts/SETAC/S9EVRsD4">SETAC</a> conference in 2010 <a class="footnote-ref" id="fnref:64" href="#fn:64"><sup>64</sup></a> revealed that, using a new GCxGC-TOF-MS, it was possible to resolve and identify a range of new compounds within such highly complex extracts. One group of compounds found to be present were tricyclic diamondoid acids.<a class="footnote-ref" id="fnref:65" href="#fn:65"><sup>65</sup></a> These structures had previously not even been considered as naphthenic acids and suggests an unprecedented degree of biodegradation of some of the oil in the <a href="/facts/Oil_sands/ewYn43lb">oil sands</a>. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Gas-liquid_chromatography/kwLY8vt1">Gas-liquid chromatography</a></li> <li><a href="/facts/Ecotoxicology/B4R4EBIb">Ecotoxicology</a></li> <li><a href="/facts/Environmental_chemistry/ByvgBKNs">Environmental chemistry</a></li> <li><a href="/facts/Toxicology/L6XHRIJH">Toxicology</a></li> <li><a href="/facts/Pollution/JRagxumQ">Pollution</a></li> <li><a href="/facts/Endocrine_disruptor/Yk2hfnTj">Endocrine disruptor</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Gough, M. A.; Rowland, S. J. (1990). "Characterization of unresolved complex mixtures of hydrocarbons in petroleum". Nature. 344 (6267). Springer Science and Business Media LLC: 648–650. Bibcode:1990Natur.344..648G. doi:10.1038/344648a0. ISSN 0028-0836. S2CID 4273041. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Gough, M. A.; Rowland, S. J. (1990). "Characterization of unresolved complex mixtures of hydrocarbons in petroleum". Nature. 344 (6267). Springer Science and Business Media LLC: 648–650. Bibcode:1990Natur.344..648G. doi:10.1038/344648a0. ISSN 0028-0836. S2CID 4273041. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Eglinton, Timothy L. (January 2016). "Citation for presentation of the 2014 C.C. Patterson Award to Christopher M. Reddy". Geochimica et Cosmochimica Acta. 172: 458–60. Bibcode:2016GeCoA.172..458E. doi:10.1016/j.gca.2015.11.035. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"High accuracy contamination estimation in hydrocarbon samples using GC×GC". patents.google.com. Google Patents. Retrieved 15 January 2025. <a href="https://patents.google.com/patent/US7805979B2/en" target="_blank">https://patents.google.com/patent/US7805979B2/en</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Eglinton, Timothy L. (January 2016). "Citation for presentation of the 2014 C.C. Patterson Award to Christopher M. Reddy". Geochimica et Cosmochimica Acta. 172: 458–60. Bibcode:2016GeCoA.172..458E. doi:10.1016/j.gca.2015.11.035. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Culbertson, Jennifer B.; Valiela, Ivan; Peacock, Emily E.; Reddy, Christopher M.; Carter, Anna; VanderKruik, Rachel (2007). "Long-term biological effects of petroleum residues on fiddler crabs in salt marshes". Marine Pollution Bulletin. 54 (7): 955–62. Bibcode:2007MarPB..54..955C. doi:10.1016/j.marpolbul.2007.02.015. hdl:1912/1802. PMID 17448504. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Culbertson, Jennifer B.; Valiela, Ivan; Pickart, Matthew; Peacock, Emily E.; Reddy, Christopher M. (9 July 2008). "Long-term consequences of residual petroleum on salt marsh grass". Journal of Applied Ecology. 45 (4): 1284–92. Bibcode:2008JApEc..45.1284C. doi:10.1111/j.1365-2664.2008.01477.x. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Eglinton, Timothy L. (January 2016). "Citation for presentation of the 2014 C.C. Patterson Award to Christopher M. Reddy". Geochimica et Cosmochimica Acta. 172: 458–60. Bibcode:2016GeCoA.172..458E. doi:10.1016/j.gca.2015.11.035. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Eglinton, Timothy L. (January 2016). "Citation for presentation of the 2014 C.C. Patterson Award to Christopher M. Reddy". Geochimica et Cosmochimica Acta. 172: 458–60. Bibcode:2016GeCoA.172..458E. doi:10.1016/j.gca.2015.11.035. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"C.C. Patterson Award". geochemsoc.org. Retrieved 11 January 2025. <a href="https://www.geochemsoc.org/honors/awards/ccpattersonaward" target="_blank">https://www.geochemsoc.org/honors/awards/ccpattersonaward</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Hentz, Daniel (20 September 2019). "Fifty years later, the West Falmouth oil spill yields lasting contributions to remediation efforts". who.edu. Woods Hole, MA: WHOI. Retrieved 14 January 2025. <a href="https://www.whoi.edu/news-insights/content/fifty-years-later-the-west-falmouth-oil-spill/" target="_blank">https://www.whoi.edu/news-insights/content/fifty-years-later-the-west-falmouth-oil-spill/</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Culbertson, Jennifer B.; Valiela, Ivan; Peacock, Emily E.; Reddy, Christopher M.; Carter, Anna; VanderKruik, Rachel (2007). "Long-term biological effects of petroleum residues on fiddler crabs in salt marshes". Marine Pollution Bulletin. 54 (7): 955–62. Bibcode:2007MarPB..54..955C. doi:10.1016/j.marpolbul.2007.02.015. hdl:1912/1802. PMID 17448504. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Culbertson, Jennifer B.; Valiela, Ivan; Pickart, Matthew; Peacock, Emily E.; Reddy, Christopher M. (9 July 2008). "Long-term consequences of residual petroleum on salt marsh grass". Journal of Applied Ecology. 45 (4): 1284–92. Bibcode:2008JApEc..45.1284C. doi:10.1111/j.1365-2664.2008.01477.x. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Reddy, Christopher M.; Eglinton, Timothy I.; Hounshell, Aubrey; White, Helen K.; Xu, Li; Gaines, Richard B.; Frysinger, Glenn S. (27 September 2002). "The West Falmouth Oil Spill after Thirty Years: The Persistence of Petroleum Hydrocarbons in Marsh Sediments". Environmental Science & Technology. 36 (22): 4754–60. Bibcode:2002EnST...36.4754R. doi:10.1021/es020656n. PMID 12487296. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Eglinton, Timothy L. (January 2016). "Citation for presentation of the 2014 C.C. Patterson Award to Christopher M. Reddy". Geochimica et Cosmochimica Acta. 172: 458–60. Bibcode:2016GeCoA.172..458E. doi:10.1016/j.gca.2015.11.035. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Rowland, Steven; Donkin, Peter; Smith, Emma; Wraige, Emma (2001). "Aromatic Hydrocarbon "Humps" in the Marine Environment: Unrecognized Toxins?". Environmental Science & Technology. 35 (13). American Chemical Society (ACS): 2640–2644. Bibcode:2001EnST...35.2640R. doi:10.1021/es0018264. ISSN 0013-936X. PMID 11452586. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>Donkin, Peter; Smith, Emma L.; Rowland, Steven J. (2003). "Toxic Effects of Unresolved Complex Mixtures of Aromatic Hydrocarbons Accumulated by Mussels,Mytilus edulis, from Contaminated Field Sites". Environmental Science & Technology. 37 (21). American Chemical Society (ACS): 4825–4830. Bibcode:2003EnST...37.4825D. doi:10.1021/es021053e. ISSN 0013-936X. PMID 14620806. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>Booth, Andy M.; Sutton, Paul A.; Lewis, C. Anthony; Lewis, Alastair C.; Scarlett, Alan; Chau, Wing; Widdows, John; Rowland, Steven J. (2007). "Unresolved Complex Mixtures of Aromatic Hydrocarbons: Thousands of Overlooked Persistent, Bioaccumulative, and Toxic Contaminants in Mussels". Environmental Science & Technology. 41 (2). American Chemical Society (ACS): 457–464. Bibcode:2007EnST...41..457B. doi:10.1021/es0615829. ISSN 0013-936X. PMID 17310707. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Scarlett, Alan; Galloway, Tamara S.; Rowland, Steven J. (2007-06-08). "Chronic toxicity of unresolved complex mixtures (UCM) of hydrocarbons in marine sediments" (PDF). Journal of Soils and Sediments. 7 (4). Springer Science and Business Media LLC: 200–206. Bibcode:2007JSoSe...7..200S. doi:10.1065/jss2007.06.232. ISSN 1439-0108. S2CID 97769416. <a href="https://d1wqtxts1xzle7.cloudfront.net/42747453/Chronic_toxicity_of_unresolved_complex_m20160216-1573-zm09cm.pdf?1455670407=&response-content-disposition=inline%3B+filename%3DChronic_toxicity_of_unresolved_complex_m.pdf" target="_blank">https://d1wqtxts1xzle7.cloudfront.net/42747453/Chronic_toxicity_of_unresolved_complex_m20160216-1573-zm09cm.pdf?1455670407=&response-content-disposition=inline%3B+filename%3DChronic_toxicity_of_unresolved_complex_m.pdf</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Scarlett, A., Rowland, S. J., Galloway, T. S., Lewis, A. C. & Booth, A. M. Chronic sublethal effects associated with branched alkylbenzenes bioaccumulated by mussels. Environmental Toxicology and Chemistry 27, 561–567 (2008). <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>Booth, A., Scarlett, A., Lewis, C. A., Belt, S. T. & Rowland, S. J. Unresolved Complex Mixtures (UCMs) of Aromatic Hydrocarbons: Branched Alkyl Indanes and Branched Alkyl Tetralins are present in UCMs and accumulated by and toxic to, the mussel Mytilus edulis. Environ Sci Technol. 42, 8122–8126 (2008). <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> <li id="fn:22"><p>Scarlett, A., Dissanayake, A., Rowland, S. J. & Galloway, T. S. Behavioral, physiological, and cellular responses following trophic transfer of toxic monoaromatic hydrocarbons. Environmental Toxicology and Chemistry 28, 381–387 (2009). <a href="#fnref:22" class="footnote-back-ref">↩</a></p></li> <li id="fn:23"><p>Tollefsen, K. E., Harman, C., Smith, A. & Thomas, K. V. Estrogen receptor (ER) agonists and androgen receptor (AR) antagonists in effluents from Norwegian North Sea oil production platforms. Marine Pollution Bulletin 54, 277–283 (2007). <a href="#fnref:23" class="footnote-back-ref">↩</a></p></li> <li id="fn:24"><p>Smith, E., Wraige, E., Donkin, P. & Rowland, S. Hydrocarbon humps in the marine environment: Synthesis, toxicity, and aqueous solubility of monoaromatic compounds. Environmental Toxicology and Chemistry 20, 2428–2432 (2001). <a href="#fnref:24" class="footnote-back-ref">↩</a></p></li> <li id="fn:25"><p>Sutton, P. A., Lewis, C. A. & Rowland, S. J. Isolation of individual hydrocarbons from the unresolved complex hydrocarbon mixture of a biodegraded crude oil using preparative capillary gas chromatography. Organic Geochemistry 36, 963–970 (2005). <a href="#fnref:25" class="footnote-back-ref">↩</a></p></li> <li id="fn:26"><p>Killops, S. D. & Killops, V. J. An introduction to organic geochemistry (Longman, Harlow, England, 1993). <a href="#fnref:26" class="footnote-back-ref">↩</a></p></li> <li id="fn:27"><p>Peters, K. E., Walters, C. C. & Moldowan, J. M. The biomarker guide: Volume 1, Biomarkers and Isotopes in the Environment and Human History (Cambridge University Press, Cambridge, England, 2005). <a href="#fnref:27" class="footnote-back-ref">↩</a></p></li> <li id="fn:28"><p>Gough, M. A.; Rowland, S. J. (1990). "Characterization of unresolved complex mixtures of hydrocarbons in petroleum". Nature. 344 (6267). Springer Science and Business Media LLC: 648–650. Bibcode:1990Natur.344..648G. doi:10.1038/344648a0. ISSN 0028-0836. S2CID 4273041. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:28" class="footnote-back-ref">↩</a></p></li> <li id="fn:29"><p>Scarlett, Alan; Galloway, Tamara S.; Rowland, Steven J. (2007-06-08). "Chronic toxicity of unresolved complex mixtures (UCM) of hydrocarbons in marine sediments" (PDF). Journal of Soils and Sediments. 7 (4). Springer Science and Business Media LLC: 200–206. Bibcode:2007JSoSe...7..200S. doi:10.1065/jss2007.06.232. ISSN 1439-0108. S2CID 97769416. <a href="https://d1wqtxts1xzle7.cloudfront.net/42747453/Chronic_toxicity_of_unresolved_complex_m20160216-1573-zm09cm.pdf?1455670407=&response-content-disposition=inline%3B+filename%3DChronic_toxicity_of_unresolved_complex_m.pdf" target="_blank">https://d1wqtxts1xzle7.cloudfront.net/42747453/Chronic_toxicity_of_unresolved_complex_m20160216-1573-zm09cm.pdf?1455670407=&response-content-disposition=inline%3B+filename%3DChronic_toxicity_of_unresolved_complex_m.pdf</a> <a href="#fnref:29" class="footnote-back-ref">↩</a></p></li> <li id="fn:30"><p>Rowland, Steven; Donkin, Peter; Smith, Emma; Wraige, Emma (2001). "Aromatic Hydrocarbon "Humps" in the Marine Environment: Unrecognized Toxins?". Environmental Science & Technology. 35 (13). American Chemical Society (ACS): 2640–2644. Bibcode:2001EnST...35.2640R. doi:10.1021/es0018264. ISSN 0013-936X. 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