Browsing by Author "W. Gregory Cope, Committee Member"

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Bioavailability of Polycyclic Aromatic Hydrocarbons in the Aquatic Environment.
(2006-03-06) White, Katrina Elizabeth; Chris Hofelt, Committee Member; Elizabeth Guthrie Nichols, Committee Member; W. Gregory Cope, Committee Member; Damian Shea, Committee Chair
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment and have been shown to elicit toxicity in humans and other organisms. Therefore, it is important to monitor environmental concentrations of PAHs. Toxicologically, we are concerned not only with the total PAH concentration but, with that fraction available to partition into an organism (bioavailable fraction). This research fits within three areas concerning bioavailability of PAHs including; 1) development of methods to measure bioavailability in the field, 2) identification and characterization of mechanisms controlling bioavailability and, 3) development of models to predict bioavailability in the natural environment. In the first phase of this research, the role of black carbon (BC) in the bioavailability of PAHs in soil and sediment was examined by measuring sorption in systems containing BC, natural organic matter (NOM), and microorganisms. A model was developed to predict the bioavailable fraction of PAHs and factors that may alter sorption in the natural environment from that predicted by laboratory models were examined. In the second phase of this research, a novel passive sampling device was developed to monitor truly dissolved PAH concentrations in water. Sorption isotherms of pyrene-d10 were measured for diesel soot (DS), Suwannee River NOM, Leonardite humic acids (HA), DS previously exposed to NOM and HA, in binary systems containing both DS and NOM, and to DS exposed to lake water. When DS was previously exposed to NOM, competition for sorption sites was observed. However, when both pyrene-d10 and NOM were introduced to DS simultaneously, less competition occurred and sorption was predicted within 92% of observed values using additive sorption models (based on the unit-normalized Freundlich model and Polyani-Dubinin-Manes model). Weathering of DS significantly reduced adsorption capacity but many strong sorption sites still remained, possibly due to renewal of sorption sites by microorganisms. This research demonstrated that sorption in the natural environment may be altered from that predicted by laboratory models due to 1) competition of linear organic carbon for sorption sites on DS, and 2) the presence of microorganisms. This research has important implications for predicting bioavailability and ecotoxicological risk of organic contaminants in soils and sediments. In the second phase of this research, I evaluated a novel passive sampling device, the polydimethyl(siloxane) (PDMS) integrative sampler, by 1) measuring the uptake and release kinetics of 48 PAHs from water into PDMS 2) comparing methods of loading performance reference compounds and 3) verifying the uptake kinetics by comparing PAH concentrations predicted by samplers to measured concentrations. Polycyclic aromatic hydrocarbons with a log K[subscript ow] 4.90 remained in the linear uptake phase for the duration of the exposure. Standard deployments of two weeks could be used for time-integrative monitoring of these compounds. Compounds with a log K[subscript ow] 4.38 reach equilibrium rapidly (T₅₀ 9 d) and the linear uptake model could not be used to predict analyte concentrations. Decreasing the surface area to volume ratio of the sampler would easily solve this issue. Surface area normalized sampling rates of PDMS samplers and semi-permeable membrane devices (SPMDs), the most commonly used passive sampling device, were similar, indicating that PDMS samplers are comparable to the SPMD. Concentrations of PAHs in the PDMS samplers predicted concentrations in water within a factor of two and on average within 30% of the actual concentration. Poly(dimethylsiloxane) samplers offer great potential for monitoring PAH exposure in the aquatic environment.
Regulatory Control of Histamine Production in North Carolina Harvested Mahi-Mahi (Coryphaena Hippurus) and Yellowfin Tuna (Thunnus Albacares): A HACCP-Based Industry Survey
(2004-07-09) Allen, Dennis Grey; David P. Green, Committee Co-Chair; W. Gregory Cope, Committee Member; Lee-Ann Jaykus, Committee Co-Chair
Histamine poisoning is one of the most common chemically induced seafood borne illnesses reported in the United States today. Generally it is believed that the causative agents are biogenic amines (histamine, putrescine and cadaverine) produced by Gram negative bacteria. Under the U.S. Food and Drug Administration's HACCP program, growth of histamine-producing bacteria in potentially hazardous fish is controlled primarily by limiting time and temperature conditions. The purpose of this study was to determine if current regulatory guidelines are being meet for the control of histamine production in North Carolina harvested mahi-mahi and yellowfin tuna, and if not, what potential food safety risks may likely occur. Twenty-nine composite fish muscle samples were obtained from 18 mahi-mahi and 11 yellowfin tuna troll-caught and analyzed for their histamine content. No sample analyzed exceeded 2 ppm histamine, the detection threshold for Neogen's ELISA-based Veratox® rapid test. Fish internal temperatures were continuously monitored from point of harvest through primary processing to determine individual fish cooling rates. Mahi-mahi were chilled on ice within 12 hrs of harvest as required under the federal HACCP guidelines. Generally, yellowfin tuna (60%) did not meet the HACCP requirement [uneviscerated tunas exceeding 20 lbs (9.1 Kg) in weight] of achieving an internal temperature of < 50oF (10oC) in 6 hrs. Three hundred and eighty-six composite fish muscle and environmental samples were screened for the presence of histamine-producing bacteria. Twenty-six percent of 549 isolates selected based on their morphological characteristics tested positive on Niven's media. Sixty-three Niven's positive isolates were Gram negative rods and 58 were Gram positive. The Beckon Dickinson BBL Crystal method was used primarily for identification of Gram positive isolates since the API 20E Enterobacteriaceae identification test is specific for the identification of Gram negative bacteria. Neither API 20E test nor BBL Crystal method was able to identify every Niven's positive isolate. Only five of forty-three isolates tested were confirmed and classified as low histamine producers (<250 ppm in 48 hrs at >15oC). Three Gram negative isolates were identified as Enterobacter cloacae. Two Gram-positive isolates were identified as Staphylococcus kloosii. This study contradicts the general belief that Gram-negative bacteria are solely responsible for histamine production in potentially hazardous fish. The confirmation of histamine-producing bacteria found in this study demonstrates the potential risk for histamine production. However, no detectable levels were found in the fish muscle samples analyzed, even though yellowfin tuna did not meet the regulatory HACCP guidelines. Therefore no food safety risks were found under commercial conditions studied.