Marirosa Molina

Variability in the distribution of lipid biomarkers and their molecular isotopic composition in Altamaha estuarine sediments : implications for the relative contribution of organic matter from various sources

The estuarine mixing zone is an effective trap for particulate and dissolved organic matter from many sources, and thus greatly affects transport and deposition of organic matter between the land and ocean. This study examined sedimentary distributions of various fatty acids and their stable isotope compositions at three sites which represent different levels of mixing in the Altamaha River estuary, Georgia, USA. Distributions of other neutral lipids (phytol, C14–C32 fatty alcohols, and two sterols) were also determined as supplementary biomarkers from various sources. Results suggest that POM from terrestrial plant material was dominant at an initial, upper estuary mixing zone (salinity in the water column is near zero but porewater in the sediment is saline) while POM from marine sources was mainly deposited at a more intensive mixing zone (wherein salinity in surface and bottom waters was identical) in the Altamaha. Much less particulate lipid was deposited in Altamaha River mouth sediments even during the high discharge season, suggesting that terrestrial plant-derived POM may not be significantly transported across the mixing zone. Analyses of fatty acid isotopic composition further verify the differential deposition pattern of POM from different sources.

Relationship and Variation of qPCR and Culturable Enterococci Estimates in Ambient Surface Waters Are Predictable

The quantitative polymerase chain reaction (qPCR) method provides rapid estimates of fecal indicator bacteria densities that have been indicated to be useful in the assessment of water quality. Primarily because this method provides faster results than standard culture-based methods, the U.S. Environmental Protection Agency is currently considering its use as a basis for revised ambient water quality criteria. In anticipation of this possibility, we sought to examine the relationship between qPCR-based and culture-based estimates of enterococci in surface waters. Using data from several research groups, we compared enterococci estimates by the two methods in water samples collected from 37 sites across the United States. A consistent linear pattern in the relationship between cell equivalents (CCE), based on the qPCR method, and colony-forming units (CFU), based on the traditional culturable method, was significant (P < 0.05) at most sites. A linearly decreasing variance of CCE with increasing CFU levels was significant (P < 0.05) or evident for all sites. Both marine and freshwater sites under continuous influence of point-source contamination tended to reveal a relatively constant proportion of CCE to CFU. The consistency in the mean and variance patterns of CCE versus CFU indicates that the relationship of results based on these two methods is more predictable at high CFU levels (e.g., log(10)CFU > 2.0/100 mL) while uncertainty increases at lower CFU values. It was further noted that the relative error in replicated qPCR estimates was generally higher than that in replicated culture counts even at relatively high target levels, suggesting a greater need for replicated analyses in the qPCR method to reduce relative error. Further studies evaluating the relationship between culture and qPCR should take into account analytical uncertainty as well as potential differences in results of these methods that may arise from sample variability, different sources of pollution, and environmental factors.

Cross-induction of pyrene and phenanthrene in a Mycobacterium sp. isolated from polycyclic aromatic hydrocarbon contaminated river sediments

A polycyclic aromatic hydrocarbon (PAH)-degrading culture enriched from contaminated river sediments and a Mycobacterium sp. isolated from the enrichment were tested to investigate the possible synergistic and antagonistic interactions affecting the degradation of pyrene in the presence of low molecular weight PAHs. The Mycobacterium sp. was able to mineralize 63% of the added pyrene when it was present as a sole source of carbon and energy. When the enrichment culture and the isolated bacterium were exposed to phenanthrene, de novo protein synthesis was not required for the rapid mineralization of pyrene, which reached 52% in chloramphenicol-treated cultures and 44% in the absence of the protein inhibitor. In the presence of chloramphenicol, < 1% of the added pyrene was mineralized by the mixed culture after exposure to anthracene and naphthalene. These compounds did not inhibit pyrene utilization when present at the same time as pyrene. Concurrent mineralization of pyrene and phenanthrene after exposure to either compound was observed. Cross-acclimation between ring classes of PAHs may be a potentially important interaction influencing the biodegradation of aromatic compounds in contaminated environments.

Characterizing relationships among fecal indicator bacteria, microbial source tracking markers, and associated waterborne pathogen occurrence in stream water and sediments in a mixed land use watershed.

Bed sediments of streams and rivers may store high concentrations of fecal indicator bacteria (FIB) and pathogens. Due to resuspension events, these contaminants can be mobilized into the water column and affect overall water quality. Other bacterial indicators such as microbial source tracking (MST) markers, developed to determine potential sources of fecal contamination, can also be resuspended from bed sediments. The primary objective of this study was to predict occurrence of waterborne pathogens in water and streambed sediments using a simple statistical model that includes traditionally measured FIB, environmental parameters and source allocation, using MST markers as predictor variables. Synoptic sampling events were conducted during baseflow conditions downstream from agricultural (AG), forested (FORS), and wastewater pollution control plant (WPCP) land uses. Concentrations of FIB and MST markers were measured in water and sediments, along with occurrences of the enteric pathogens Campylobacter, Listeria and Salmonella, and the virulence gene that carries Shiga toxin, stx2. Pathogens were detected in water more often than in underlying sediments. Shiga toxin was significantly related to land use, with concentrations of the ruminant marker selected as an independent variable that could correctly classify 76% and 64% of observed Shiga toxin occurrences in water and sediment, respectively. FIB concentrations and water quality parameters were also selected as independent variables that correctly classified Shiga toxin occurrences in water and sediment (54%-87%), and Salmonella occurrences in water (96%). Relationships between pathogens and indicator variables were generally inconsistent and no single indicator adequately described occurrence of all pathogens. Because of inconsistent relationships between individual pathogens and FIB/MST markers, incorporating a combination of FIB, water quality measurements, and MST markers may be the best way to assess microbial water quality in mixed land use systems.

Microbial community dynamics and evaluation of bioremediation strategies in oil-impacted salt marsh sediment microcosms

Microbial community dynamics in wetlands microcosms emended with commercial products (surfactant, a biological agent, and nutrients) designed to enhance bioremediation was followed for 3 months. The effectiveness of enhanced degradation was assessed by determining residual concentrations of individual petroleum hydrocarbons by GC/MS. The size and composition of the sediment microbial community was assessed using a variety of indices, including bacterial plate counts, MPNs, and DNA hybridizations with domain- and group-specific oligonucleotide probes. The addition of inorganic nutrients was the most effective treatment for the enhancement of oil degradation, resulting in marked degradation of petroleum alkanes and a lesser extent of degradation of aromatic oil constituents. The enhanced degradation was associated with increases in the amount of extractable microbial DNA and Streptomyces in the sediment, although not with increased viable counts (plate counts, MPN). Bacteria introduced with one of the proprietary products were still detected in the microcosms after 3 months, but were not a major quantitative constituent of the community. The biological product enhanced oil degradation relative to the control, but to a lesser extent than the nutrient additions alone. In contrast, application of the surfactant to the oil-impacted sediment decreased oil degradation. Journal of Industrial Microbiology & Biotechnology (2001) 27, 72–79.

Decay of Fecal Indicator Bacterial Populations and Bovine-Associated Source-Tracking Markers in Freshly Deposited Cow Pats

ABSTRACT Understanding the survival of fecal indicator bacteria (FIB) and microbial source-tracking (MST) markers is critical to developing pathogen fate and transport models. Although pathogen survival in water microcosms and manure-amended soils is well documented, little is known about their survival in intact cow pats deposited on pastures. We conducted a study to determine decay rates of fecal indicator bacteria (Escherichia coli and enterococci) and bovine-associated MST markers (CowM3, Rum-2-bac, and GenBac) in 18 freshly deposited cattle feces from three farms in northern Georgia. Samples were randomly assigned to shaded or unshaded treatment in order to determine the effects of sunlight, moisture, and temperature on decay rates. A general linear model (GLM) framework was used to determine decay rates. Shading significantly decreased the decay rate of the E. coli population (P < 0.0001), with a rate of −0.176 day−1 for the shaded treatment and −0.297 day−1 for the unshaded treatment. Shading had no significant effect on decay rates of enterococci, CowM3, Rum-2-bac, and GenBac (P > 0.05). In addition, E. coli populations showed a significant growth rate (0.881 day−1) in the unshaded samples during the first 5 days after deposition. UV-B was the most important parameter explaining the decay rate of E. coli populations. A comparison of the decay behaviors among all markers indicated that enterococcus concentrations exhibit a better correlation with the MST markers than E. coli concentrations. Our results indicate that bovine-associated MST markers can survive in cow pats for at least 1 month after excretion, and although their decay dynamic differs from the decay dynamic of E. coli populations, they seem to be reliable markers to use in combination with enterococci to monitor fecal pollution from pasture lands.

Temporal Assessment of the Impact of Exposure to Cow Feces in Two Watersheds by Multiple Host-Specific PCR Assays

ABSTRACT Exposure to feces in two watersheds with different management histories was assessed by tracking cattle feces bacterial populations using multiple host-specific PCR assays. In addition, environmental factors affecting the occurrence of these markers were identified. Each assay was performed using DNA extracts from water and sediment samples collected from a watershed directly impacted by cattle fecal pollution (WS1) and from a watershed impacted only through runoff (WS2). In WS1, the ruminant-specific Bacteroidales 16S rRNA gene marker CF128F was detected in 65% of the water samples, while the non-16S rRNA gene markers Bac1, Bac2, and Bac5 were found in 32 to 37% of the water samples. In contrast, all source-specific markers were detected in less than 6% of the water samples from WS2. Binary logistic regressions (BLRs) revealed that the occurrence of Bac32F and CF128F was significantly correlated with season as a temporal factor and watershed as a site factor. BLRs also indicated that the dynamics of fecal-source-tracking markers correlated with the density of a traditional fecal indicator (P < 0.001). Overall, our results suggest that a combination of 16S rRNA gene and non-16S rRNA gene markers provides a higher level of confidence for tracking unknown sources of fecal pollution in environmental samples. This study also provided practical insights for implementation of microbial source-tracking practices to determine sources of fecal pollution and the influence of environmental variables on the occurrence of source-specific markers.

Estimated human health risks from recreational exposures to stormwater runoff containing animal faecal material

Scientific evidence supporting recreational water quality benchmarks primarily stems from epidemiological studies conducted at beaches impacted by human fecal sources. Epidemiological studies conducted at locations impacted by non-human faecal sources have provided ambiguous and inconsistent estimates of risk. Quantitative Microbial Risk Assessment (QMRA) is another tool to evaluate potential human health risks from recreational exposures to non-human faecal contamination. The potential risk differential between human and selected non-human faecal sources has been characterized previously for direct deposition of animal feces to water. In this evaluation, we examine the human illness potential from a recreational exposure to freshwater impacted by rainfall-induced runoff containing agricultural animal faecal material. Risks associated with these sources would be at least an order of magnitude lower than the benchmark level of public health protection associated with current US recreational water quality criteria, which are based on contamination from human sewage sources. We examine the human illness potential from exposure to rainfall-induced runoff.The predicted risks are lower than the benchmark level of protection.This risk assessment should be helpful to inform public health decision-making.

Using the Q10 model to simulate E. coli survival in cowpats on grazing lands

Microbiological quality of surface waters can be affected by microbial load in runoff from grazing lands. This effect, with other factors, depends on the survival of microorganisms in animal waste deposited on pastures. Since temperature is a leading environmental parameter affecting survival, it indirectly impacts water microbial quality. The Q10 model is widely used to predict the effect of temperature on rates of biological processes, including survival. Objectives of this work were to (i) evaluate the applicability of the Q10 model to Escherichia coli inactivation in bovine manure deposited on grazing land (i.e., cowpats) and (ii) identify explanatory variables for the previously reported E. coli survival dynamics in cowpats. Data utilized in this study include published results on E. coli concentrations in natural and repacked cowpats from research conducted the U.S. (Virginia and Maryland), New Zealand, and the United Kingdom. Inspection of the datasets led to conceptualizing E. coli survival (in cowpats) as a two-stage process, in which the initial stage was due to growth, inactivation or stationary state of the population and the second stage was the approximately first-order inactivation. Applying the Q10 model to these datasets showed a remarkable similarity in inactivation rates, using the thermal time. The reference inactivation rate constant of 0.042 (thermal days)(-1) at 20 °C gave a good approximation (R(2)=0.88) of all inactivation stage data with Q10=1.48. The reference inactivation rate constants in individual studies were no different from the one obtained by pooling all data (P<0.05). The rate of logarithm of the E. coli concentration change during the first stage depended on temperature. Duration of the first stage, prior to the first-order inactivation stage and the initial concentration of E. coli in cowpats, could not be predicted from available data. Diet and age are probable factors affecting these two parameters however, until their environmental and management predictors are known, microbial water quality modeling must treat them as a stochastic source of uncertainty in simulation results.

An integrated environmental modeling framework for performing Quantitative Microbial Risk Assessments

Standardized methods are often used to assess the likelihood of a human-health effect from exposure to a specified hazard, and inform opinions and decisions about risk management and communication. A Quantitative Microbial Risk Assessment (QMRA) is specifically adapted to detail potential human-health risks from exposure to pathogens; it can include fate and transport models for various media, including the source zone (initial fecal release), air, soil/land surface, surface water, vadose zone and aquifer. The analysis step of a QMRA can be expressed as a system of computer-based data delivery and modeling that integrates interdisciplinary, multiple media, exposure and effects models and databases. Although QMRA does not preclude using source-term and fate and transport models, it is applied most commonly where the source-term is represented by the receptor location (i.e., exposure point), so the full extent of exposure scenarios has not been rigorously modeled. An integrated environmental modeling infrastructure is, therefore, ideally suited to include fate and transport considerations and link the risk assessment paradigm between source and receptor seamlessly. A primary benefit of the source-to-outcome approach is that it allows an expanded view of relevant cause-and-effect relationships, which facilitate consideration of management options related to source terms and their fate and transport pathways. The Framework for Risk Analysis in Multimedia Environmental Systems (FRAMES) provides software technology for analysts to insert appropriate models and databases that fit the problem statement and design and construct QMRAs that are reproducible, flexible, transferable, reusable, and transparent. A sample application using different models and databases registered with FRAMES is presented. It illustrates how models are linked to assess six different manure-based contaminant sources, following three pathogens (Salmonella eterica, Cryptosporidium spp., and Escherichia coli O157:H7) to a receptor where exposures and health risk impacts are then evaluated. The modeling infrastructure demonstrates how analysts could use the system to discern which pathogens might be important and when, and which sources could contribute to their importance. IEM FRAMES is a flexible tool to support custom-designed source-to-receptor QMRAs.FRAMES captures multiple and user-defined modeling approaches.An example QMRA assesses source apportionment and pathogens of importance.Pathogen fate and transport modeling is linked to point-of-exposure risk analysis.IEM links environmental and microbial characteristics with an uncertainty analysis.