A method for using polyethylene passive samplers to measure polycyclic aromatic hydrocarbon chemical activity in sediments

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2005.Includes bibliographical references.In order to aid in the determination of the hazards posed by hydrophobic organic compounds (HOCs) in sediment beds, a method for the use of polyethylene (PE) sheets as passive sampling devices for measuring chemical activities was explored. A model which depends on a concentration gradient and two mass transfer limiting zones in series was used. Internal tracer chemicals within the polyethylene devices (PEDs) were used to calibrate the mass transfer model which can have different mass transfer coefficients depending on the site and target chemicals being investigated. The model allowed for the measurement of HOC chemical activities by measuring the change of mass of tracer and target chemical within the PED, and knowing the PE-water partitioning coefficient, ..., and the liquid solubility, ..., of the target chemical. The method was tested using PEDs impregnated with dlO-phenanthrene and dlO-pyrene. First, PEDs were used to measure known concentrations of phenanthrene and fluoranthene in stirred seawaters. Seeing that the PEDs performed well, returning results which were within 25% of the known chemical activities, PEDs were then tested for measuring phenanthrene, fluoranthene, and pyrene in Boston Harbor sediments.(cont.) Porewaters of Boston Harbor sediments were extracted as a benchmark against which to assess the performance of three methods for measuring sediment chemical activities: (1) PEDs using impregnated tracers exposed for 52 and 92 days to simulated sediment beds, (2) sediment extractions and an equilibrium partitioning model as recommended by EPA for determining sediment benchmarks, and (3) PE samplers brought to equilibrium with sediment slurries. The results of this study showed that the two methods using PE passive samplers produced measurements which were within a factor of 2 of the porewater extraction results. The equilibrium partitioning model, however, produced results which were at least an order of magnitude different from the measurements of the other methods. Future work on PEDs is needed to develop faster response times and internal standards which will allow for the measurement of a more diverse set of HOCs.by Loretta A. Fernandez.S.M

Polyethylene passive samplers for measuring hydrophobic organic chemical concentrations in sediment porewaters and their use in predicting bioaccumulation in soft-shell clams (Mya arenaria) from sites near Boston, MA

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references.In order to determine the hazards posed by hydrophobic organic compounds (HOCs) in sediment beds, the following areas of research were explored: (1) the use of polyethylene (PE) sheets as passive sampling devices in sediments, using performance reference compounds (PRCs) in order to reduce deployment times to the order of days, (2) the use of limited PRC data to calibrate mass-transfer models for the exchange of a suite of compounds between polymer strips and sedimentary porous media, and (3) the use of in-situ passive sampling methods to deduce chemical activities of HOCs in sediments and the tissues of soft shelled clams (Mya arenaria) , in order to measure bioaccumulation potential. First, the use of PE passive samplers, in-situ, to measure freely dissolved HOC concentrations, is demonstrated. PRCs, impregnated into the PE before use, allow porewater concentrations to be deduced after exposure times much shorter than would be required for sampler equilibration (days instead of months). Next, the method is expanded for measuring suites of compounds of the same class. A one-dimensional diffusion model of chemical exchange between a polymer sheet of finite thickness and an unmixed sediment bed is employed. Porewater concentrations for seventeen polycyclic aromatic hydrocarbons (PAHs) are measured using samplers deployed for 3 to 10 days in homogenized sediment from a coal-tar contaminated site. Finally, the samplers are used to determine the potential for HOCs to bioaccumulate in Mya arenaria in sediments from six sites near Boston, MA. PE-deduced porewater PAH concentrations are compared to lipid-normalized tissue PAH concentrations in samples taken from twelve stations distributed throughout the sites. Additionally, tissue concentrations are compared to bulk sediment concentrations and porewater concentrations deduced from equilibrium partitioning models that include sorption to both organic carbon and black carbon fractions. Results show correlations only between PE-deduced porewater concentrations and tissue concentrations, illustrating the usefulness of PE passive samplers for gauging risk to benthic organisms associated with HOC contaminated sediments. Also, porewater concentrations estimated using equilibrium partitioning methods overestimated porewater concentrations by one to three orders of magnitude at all but one site.by Loretta A. Fernandez.Ph.D

Effect of Hydrocortisone on Mortality and Organ Support in Patients With Severe COVID-19: The REMAP-CAP COVID-19 Corticosteroid Domain Randomized Clinical Trial.

Importance: Evidence regarding corticosteroid use for severe coronavirus disease 2019 (COVID-19) is limited. Objective: To determine whether hydrocortisone improves outcome for patients with severe COVID-19. Design, Setting, and Participants: An ongoing adaptive platform trial testing multiple interventions within multiple therapeutic domains, for example, antiviral agents, corticosteroids, or immunoglobulin. Between March 9 and June 17, 2020, 614 adult patients with suspected or confirmed COVID-19 were enrolled and randomized within at least 1 domain following admission to an intensive care unit (ICU) for respiratory or cardiovascular organ support at 121 sites in 8 countries. Of these, 403 were randomized to open-label interventions within the corticosteroid domain. The domain was halted after results from another trial were released. Follow-up ended August 12, 2020. Interventions: The corticosteroid domain randomized participants to a fixed 7-day course of intravenous hydrocortisone (50 mg or 100 mg every 6 hours) (n = 143), a shock-dependent course (50 mg every 6 hours when shock was clinically evident) (n = 152), or no hydrocortisone (n = 108). Main Outcomes and Measures: The primary end point was organ support-free days (days alive and free of ICU-based respiratory or cardiovascular support) within 21 days, where patients who died were assigned -1 day. The primary analysis was a bayesian cumulative logistic model that included all patients enrolled with severe COVID-19, adjusting for age, sex, site, region, time, assignment to interventions within other domains, and domain and intervention eligibility. Superiority was defined as the posterior probability of an odds ratio greater than 1 (threshold for trial conclusion of superiority >99%). Results: After excluding 19 participants who withdrew consent, there were 384 patients (mean age, 60 years; 29% female) randomized to the fixed-dose (n = 137), shock-dependent (n = 146), and no (n = 101) hydrocortisone groups; 379 (99%) completed the study and were included in the analysis. The mean age for the 3 groups ranged between 59.5 and 60.4 years; most patients were male (range, 70.6%-71.5%); mean body mass index ranged between 29.7 and 30.9; and patients receiving mechanical ventilation ranged between 50.0% and 63.5%. For the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively, the median organ support-free days were 0 (IQR, -1 to 15), 0 (IQR, -1 to 13), and 0 (-1 to 11) days (composed of 30%, 26%, and 33% mortality rates and 11.5, 9.5, and 6 median organ support-free days among survivors). The median adjusted odds ratio and bayesian probability of superiority were 1.43 (95% credible interval, 0.91-2.27) and 93% for fixed-dose hydrocortisone, respectively, and were 1.22 (95% credible interval, 0.76-1.94) and 80% for shock-dependent hydrocortisone compared with no hydrocortisone. Serious adverse events were reported in 4 (3%), 5 (3%), and 1 (1%) patients in the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively. Conclusions and Relevance: Among patients with severe COVID-19, treatment with a 7-day fixed-dose course of hydrocortisone or shock-dependent dosing of hydrocortisone, compared with no hydrocortisone, resulted in 93% and 80% probabilities of superiority with regard to the odds of improvement in organ support-free days within 21 days. However, the trial was stopped early and no treatment strategy met prespecified criteria for statistical superiority, precluding definitive conclusions. Trial Registration: ClinicalTrials.gov Identifier: NCT02735707