Ingrid Padilla

Urinary phthalate metabolite concentrations among pregnant women in Northern Puerto Rico: Distribution, temporal variability, and predictors

BACKGROUND Phthalate contamination exists in the North Coast karst aquifer system in Puerto Rico. In light of potential health impacts associated with phthalate exposure, targeted action for elimination of exposure sources may be warranted, especially for sensitive populations such as pregnant women. However, information on exposure to phthalates from a variety of sources in Puerto Rico is lacking. The objective of this study was to determine concentrations and predictors of urinary phthalate biomarkers measured at multiple times during pregnancy among women living in the Northern karst area of Puerto Rico. METHODS We recruited 139 pregnant women in Northern Puerto Rico and collected urine samples and questionnaire data at three separate visits (18 ± 2 weeks, 22 ± 2 weeks, and 26 ± 2 weeks of gestation). Urine samples were analyzed for eleven phthalate metabolites: mono-2-ethylhexyl phthalate (MEHP), mono-2-ethyl-5-hydroxyhexyl phthalate, mono-2-ethyl-5-oxohexyl phthalate, mono-2-ethyl-5-carboxypentyl phthalate, mono-ethyl phthalate (MEP), mono-n-butyl phthalate, mono-benzyl phthalate, mono-isobutyl phthalate, mono-3-carboxypropyl phthalate (MCPP), mono carboxyisononyl phthalate (MCNP), and mono carboxyisooctyl phthalate (MCOP). RESULTS Detectable concentrations of phthalate metabolites among pregnant women living in Puerto Rico was prevalent, and metabolite concentrations tended to be higher than or similar to those measured in women of reproductive age from the general US population. Intraclass correlation coefficients ranged from very weak (MCNP; 0.05) to moderate (MEP; 0.44) reproducibility among all phthalate metabolites. We observed significant or suggestive positive associations between urinary phthalate metabolite concentrations and water usage/storage habits (MEP, MCNP, MCOP), use of personal care products (MEP), and consumption of certain food items (MCPP, MCNP, and MCOP). CONCLUSIONS To our knowledge this is the first study to report concentrations, temporal variability, and predictors of phthalate biomarkers among pregnant women in Puerto Rico. Preliminary results suggest several potentially important exposure sources to phthalates in this population and future analysis from this ongoing prospective cohort will help to inform targeted approaches to reduce exposure.

Review: Groundwater flow and transport modeling of karst aquifers, with particular reference to the North Coast Limestone aquifer system of Puerto Rico

Karst systems have a high degree of heterogeneity and anisotropy, which makes them behave very differently from other aquifers. Slow seepage through the rock matrix and fast flow through conduits and fractures result in a high variation in spring response to precipitation events. Contaminant storage occurs in the rock matrix and epikarst, but contaminant transport occurs mostly along preferential pathways that are typically inaccessible locations, which makes modeling of karst systems challenging. Computer models for understanding and predicting hydraulics and contaminant transport in aquifers make assumptions about the distribution and hydraulic properties of geologic features that may not always apply to karst aquifers. This paper reviews the basic concepts, mathematical descriptions, and modeling approaches for karst systems. The North Coast Limestone aquifer system of Puerto Rico (USA) is introduced as a case study to illustrate and discuss the application of groundwater models in karst aquifer systems to evaluate aquifer contamination.RésuméLes systèmes karstiques ont un grand degré d’hétérogénéité et d’anisotropie, qui les fait se comporter de façon très différente des autres aquifères. D’une lente infiltration à travers la matrice rocheuse et d’un flux rapide à travers les conduits et fractures résulte une grande variation dans la réponse de la source aux événements pluvieux. Une rétention de polluant a lieu dans la matrice rocheuse et dans l’épikarst, mais le transport de polluants a lieu principalement suivant des cheminements préférentiels qui sont typiquement localisés de façons inaccessibles, ce qui fait de la modélisation des systèmes karstiques un challenge. Les modèles informatiques pour la compréhension et la prévision dynamique du transport du polluant dans les aquifères font que les hypothèses sur la distribution des structures géologiques et leurs propriétés hydrauliques peuvent ne pas toujours s’appliquer aux aquifères karstiques. Cet article passe en revue les concepts basiques, descriptions mathématiques et approches de modélisation des systèmes karstiques. Le système aquifère Calcaire Côtier Nord de Porto-Rico (USA) est introduit comme cas d’étude pour illustrer et discuter de l’application des modèles d’aquifères aux systèmes karstiques pour en évaluer la contamination.ZusammenfassungKarstsysteme sind hochgradig heterogen und anisotrop, weshalb ihr Verhalten sich sehr von anderen Grundwasserleitern unterscheidet. Langsames Durchsickern der Gesteinsmatrix und schnelles Durchfließen von Karströhren und Klüften führen zu einer hohen Variabilität der Reaktion von Quellen auf Niederschlagsereignisse. Die Speicherung von Schadstoffen findet in der Gesteinsmatrix und im Epikarst statt, der Transport von Schadstoffen hingegen überwiegend entlang von präferenziellen Fließwegen. Weil diese in der Regel unzugänglich sind, ist die Modellierung von Karstsystemen eine Herausforderung. Computermodelle zum Verständnis und zur Vorhersage der Hydraulik und des Schadstofftransports in Grundwasserleitern machen Annahmen über die Verteilung der hydraulischen Eigenschaften von geologischen Strukturen, die in Karstgrundwasserleitern nicht unbedingt gültig sind. Dieser Beitrag bespricht grundlegende Konzepte, mathematische Beschreibungen und Ansätze zur Modellierung von Karstgrundwasserleitern. Das North Coast Limestone Grundwassersystem in Puerto Rico (USA) wird als Fallbeispiel vorgestellt, um die Anwendung von Grundwassermodellen zur Beurteilung von Grundwasserverschmutzungen in Karstsystemen zu veranschaulichen und zu diskutieren.ResumenLos sistemas kársticos tienen un alto grado de heterogeneidad y anisotropía, lo que los hace que se comporten muy diferentes de otros acuíferos. El escurrimiento lento a través de la matriz de la roca y el flujo rápido a través de los conductos y fracturas dan como resultado una alta variación en la respuesta de los manantiales a los eventos de precipitación. El almacenamiento de los contaminantes ocurre en la matriz de la roca y en el epikarstico, pero el transporte de contaminantes ocurre mayormente a lo largo de trayectorias preferenciales que son de ubicación típicamente inaccesibles, lo cual convierte al modelado de los sistemas kársticas en un desafío. Los modelos de computadoras para entender y predecir el transporte hidráulico y de contaminantes en acuíferos hacen suposiciones acerca de la distribución y propiedades hidráulicas de los aspectos geológicos que no pueden siempre aplicarse a acuíferos kársticos. Este trabajo revisa los conceptos básicos, las descripciones matemáticas, y los enfoques de modelados para sistemas kársticas. Se introduce el sistema acuífero de North Coast Limestone de Puerto Rico (EEUU) como un caso de estudio para ilustrar y discutir la aplicación de modelos de agua subterránea en sistemas acuíferos kársticas para evaluar la contaminación del acuífero.摘要岩溶系统具有高度的非均质性与各向异性,这使得它与其它含水层的差别很大。流过岩石介质的慢速流与流过导水管道和裂隙的快速流导致泉对降水事件的响应大有不同。污染物储存在岩石介质和表层岩溶中,但污染物的迁移大多沿着优先流径发生,通常情况下这样的优先流径都处于人力无法达到的地方,这给岩溶含水层系统的模拟带来了很大的挑战。为了了解和预测含水层的水力学特性和污染物的迁移,电脑模型会假设地质体的分布和水力学性质,然而这种假设并不总能应用到岩溶含水层中。本文综述了可用于岩溶含水层的基本概念、数学描述方法与模拟方法。波多黎各(美国)的北海岸灰岩含水层系统作为本文一个实例,解释并讨论了应用地下水模型评估岩溶含水层系统中的污染。ResumoOs sistemas cársicos têm um elevado grau de heterogeneidade e anisotropia, o que faz com que se comportem de maneira muito diferente da dos outros aquíferos. O escoamento lento através da matriz da rocha e o rápido fluxo através de condutas e de fraturas resulta numa elevada variação das respostas das emergências a eventos de precipitação. O armazenamento de contaminantes ocorre na matriz da rocha e no epicarso, mas o transporte de contaminantes ocorre principalmente ao longo de caminhos preferenciais, que são tipicamente locais inacessíveis, o que faz da modelação de sistemas cársicos um desafio. Os modelos de computador, para entenderem e preverem a hidráulica e o transporte de contaminantes em aquíferos, assumem suposições sobre a distribuição e as propriedades hidráulicas das caraterísticas geológicas, as quais nem sempre podem ser aplicadas aos aquíferos cársicos. Este trabalho faz a revisão dos conceitos básicos, das descrições matemáticas e das abordagens de modelação de sistemas cársicos. O sistema aquífero Carbonatado do Litoral Norte de Porto Rico (EUA) é apresentado como um caso de estudo, de forma a ilustrar e discutir a aplicação de modelos de águas subterrâneas em sistemas aquíferos cársicos para avaliação da contaminação de aquíferos.

Electrochemically Induced Dual Reactive Barriers for Transformation of TCE and Mixture of Contaminants in Groundwater

A novel reactive electrochemical flow system consisting of an iron anode and a porous cathode is proposed for the remediation of mixture of contaminants in groundwater. The system consists of a series of sequentially arranged electrodes, a perforated iron anode, a porous copper cathode followed by a mesh-type mixed metal oxide anode. The iron anode generates ferrous species and a chemically reducing environment, the porous cathode provides a reactive electrochemically reducing barrier, and the inert anode provides protons and oxygen to neutralize the system. The redox conditions of the electrolyte flowing through this system can be regulated by controlling the distribution of the electric current. Column experiments are conducted to evaluate the process and study the variables. The electrochemical reduction on a copper foam cathode produced an electrode-based reductive potential capable of reducing TCE and nitrate. Rational electrodes arrangement, longer residence time of electrolytes and higher surface area of the foam electrode improve the reductive transformation of TCE. More than 82.2% TCE removal efficiency is achieved for the case of low influent concentration (<7.5 mg/L) and high current (>45 mA). The ferrous species produced from the iron anode not only enhance the transformation of TCE on the cathode, but also facilitates transformation of other contaminants including dichromate, selenate and arsenite. Removal efficiencies greater than 80% are achieved for these contaminants in flowing contaminated water. The overall system, comprising the electrode-based and electrolyte-based barriers, can be engineered as a versatile and integrated remedial method for a relatively wide spectrum of contaminants and their mixtures.

Estimating preferential flow in karstic aquifers using statistical mixed models.

Karst aquifers are highly productive groundwater systems often associated with conduit flow. These systems can be highly vulnerable to contamination, resulting in a high potential for contaminant exposure to humans and ecosystems. This work develops statistical models to spatially characterize flow and transport patterns in karstified limestone and determines the effect of aquifer flow rates on these patterns. A laboratory-scale Geo-HydroBed model is used to simulate flow and transport processes in a karstic limestone unit. The model consists of stainless steel tanks containing a karstified limestone block collected from a karst aquifer formation in northern Puerto Rico. Experimental work involves making a series of flow and tracer injections, while monitoring hydraulic and tracer response spatially and temporally. Statistical mixed models (SMMs) are applied to hydraulic data to determine likely pathways of preferential flow in the limestone units. The models indicate a highly heterogeneous system with dominant, flow-dependent preferential flow regions. Results indicate that regions of preferential flow tend to expand at higher groundwater flow rates, suggesting a greater volume of the system being flushed by flowing water at higher rates. Spatial and temporal distribution of tracer concentrations indicates the presence of conduit-like and diffuse flow transport in the system, supporting the notion of both combined transport mechanisms in the limestone unit. The temporal response of tracer concentrations at different locations in the model coincide with, and confirms the preferential flow distribution generated with the SMMs used in the study.

Equivalent Porous Media (EPM) Simulation of Groundwater Hydraulics and Contaminant Transport in Karst Aquifers

Karst aquifers have a high degree of heterogeneity and anisotropy in their geologic and hydrogeologic properties which makes predicting their behavior difficult. This paper evaluates the application of the Equivalent Porous Media (EPM) approach to simulate groundwater hydraulics and contaminant transport in karst aquifers using an example from the North Coast limestone aquifer system in Puerto Rico. The goal is to evaluate if the EPM approach, which approximates the karst features with a conceptualized, equivalent continuous medium, is feasible for an actual project, based on available data and the study scale and purpose. Existing National Oceanic Atmospheric Administration (NOAA) data and previous hydrogeological U. S. Geological Survey (USGS) studies were used to define the model input parameters. Hydraulic conductivity and specific yield were estimated using measured groundwater heads over the study area and further calibrated against continuous water level data of three USGS observation wells. The water-table fluctuation results indicate that the model can practically reflect the steady-state groundwater hydraulics (normalized RMSE of 12.4%) and long-term variability (normalized RMSE of 3.0%) at regional and intermediate scales and can be applied to predict future water table behavior under different hydrogeological conditions. The application of the EPM approach to simulate transport is limited because it does not directly consider possible irregular conduit flow pathways. However, the results from the present study suggest that the EPM approach is capable to reproduce the spreading of a TCE plume at intermediate scales with sufficient accuracy (normalized RMSE of 8.45%) for groundwater resources management and the planning of contamination mitigation strategies.

Electrode effects on temporal changes in electrolyte pH and redox potential for water treatment

The performance of electrochemical remediation methods could be optimized by controlling the physicochemical conditions of the electrochemical redox system. The effects of anode type (reactive or inert), current density and electrolyte composition on the temporal changes in pH and redox potential of the electrolyte were evaluated in divided and mixed electrolytes. Two types of electrodes were used: iron as a reactive electrode and mixed metal oxide coated titanium (MMO) as an inert electrode. Electric currents of 15, 30, 45 and 60 mA (37.5 mA L−1, 75 mA L−1, 112.5 mA L−1 and 150 mA L−1) were applied. Solutions of NaCl, Na2SO4 and NaHCO3 were selected to mimic different wastewater or groundwater compositions. Iron anodes resulted in highly reducing electrolyte conditions compared to inert anodes. Electrolyte pH was dependent on electrode type, electrolyte composition and current density. The pH of mixed-electrolyte was stable when MMO electrodes were used. When iron electrodes were used, the pH of electrolyte with relatively low current density (37.5 mA L−1) did not show significant changes but the pH increased sharply for relatively high current density (150 mA L−1). Sulfate solution showed more basic and relatively more reducing electrolyte conditions compared to bicarbonate and chloride solution. The study shows that a highly reducing environment could be achieved using iron anodes in divided or mixed electrolytes and the pH and redox potential could be optimized using appropriate current and polarity reversal.

Sociodemographic patterns of household water-use costs in Puerto Rico

Variability of household water-use costs across different sociodemographic groups in Puerto Rico is evaluated using census microdata from the Integrated Public Use Microdata Series (IPUMS). Multivariate analyses such as multiple linear regression (MLR) and factor analysis (FA) are used to classify, extract and interpret the household water-use costs. The FA results suggest two principal varifactors in explaining the variability of household water-use costs (64% in 2000 and 50% in 2010), which are grouped into a soft coefficient (social, economic and demographic characteristics of household residents, i.e., age, size, income, education) and a hard coefficient (dwelling conditions, i.e., number of rooms, units in the building, building age). The demographic profile of a high water-use household in Puerto Rico tends to be that of renters, people who live in larger or older buildings, people living in metro areas, or those with higher education level and higher income. The findings and discussions from this study will help decision makers to plan holistic and integrated water management to achieve water sustainability.

Spatiotemporal Response of CVOC Contamination and Remedial Actions in Eogenetic Karst Aquifers

The northern karst region of Puerto Rico has a long and extensive history of toxic spills, chemical waste, and industrial solvent release into the subsurface. High potential for exposure in the region has prompted aggressive remediation measures, which have extended for over 40 years. Of particular concern is contamination with chlorinated volatile organic compounds (CVOCs) because of their ubiquitous presence and potential health impacts. This work evaluates historical groundwater quality data to assess the spatiotemporal distribution of CVOC contamination in the karst aquifer system of northern Puerto Rico, and its response to remedial action in two superfund sites contaminated with CVOCs. Historical data collected from different information sources with different monitoring objectives is evaluated spatially and temporally using Geographic Information System (GIS) and statistical analysis. The analysis shows a significant extent of contamination that comes from multiple sources and spreads beyond the demarked sources of pollution. CVOCs are detected in 65% of all samples and 78% of all sampled wells. Groundwater shows continued level of contamination over long periods of time, demonstrating a strong capacity of the karst groundwater system to store and slowly release contamination. Trichloroethene and Tetrachloroethene are the most frequently found, although other CVOCs (e.g., Trichloromethane, Dichloromethane, Carbon Tetrachloride) are detected as well. The spatial and temporal distributions of CVOCs seem to be highly dependent upon the monitoring scheme and objectives, indicating that the data does not adequately capture the contamination plumes. Targeted remedial action using pump and treat (air stripping) and soil vapor extraction in two superfund sites has reduced concentrations over time, but the spatial and temporal extent of the contamination reflect inability to completely capture the heterogeneous plumes. Introduction and Background The northern karst region (Figure 1) contains two of the most extensive and productive freshwater aquifers in Puerto Rico (Lugo et al., 2001). These aquifers promote industrial, agricultural, and population growth (PRDNER, 2008), and contribute to the ecological integrity of the rivers, springs, wetlands, and estuaries (Padilla et al., 2011). The northern karst aquifer system comprises three major hydrogeological units (Figure 1): the upper aquifer, which is mainly composed of the Aymamon and Aguada Limestone Members; the lower aquifer, which is formed by the Lares and Montebello Limestone Members; and a confining unit that separates the upper and lower aquifer, which is comprised by the Cibao formation. (Renken et al., 2002). The upper aquifer is unconfined and also linked to the surface throughout most of its outcrop area. The lower aquifer is confined toward the coastal zone and outcrops to the south of the shallow aquifer, where it is recharged. The outcrop extents are much more vulnerable to contamination due to direct interaction with the surface. The karst aquifers of northern Puerto Rico have developed in carbonate rocks that have not undergone deep burial and are under active meteoritic diagenesis, thus considered eogenetic aquifers (Vacher and Mylroie, 2002). In addition to well-developed conduit networks, these aquifers have high primary porosity and permeability and significant flow components through the rock matrix. As a result, both conduit and matrix flow contribute flow in these aquifers. These flow characteristics allow for extensive water production from the aquifers and make the systems highly vulnerable to pollution (Göppert and Goldscheider, 2008). The highly heterogeneous distribution of flow characteristics in karst systems also imparts an enormous capacity to store and convey contaminants from sources to potential expoIngrid Y. Padilla Department of Civil Engineering, University of Puerto Rico, Mayagüez, PR, 00681, ingrid.padilla@upr.edu Vilda L. Rivera Department of Civil Engineering, University of Puerto Rico, Mayagüez, PR, 00681, vilda.riverade@upr.edu Celys Irizarry Department of Civil Engineering, University of Puerto Rico, Mayagüez, PR, 00681, celys.irizarry@upr.edu

Case Study–Puerto Rico Test Site for Exploring Contamination Threats

Puerto Rico has one of the highest densities of Superfund and National Priority List sites per square mile. The specific pollutants in those sites have been well documented and monitored over time. Puerto Rico has its share of public health problems as it has the highest rates of preterm birth compared to other jurisdiction in the US. Other important attributes, such as the stability and diversity of the population, and the presence of a karst environment with a major aquifer that provides most of the water supply to the study area, make Puerto Rico a good case study to evaluate the impact of exposure to contamination on public health problems. In this paper, we present an interdisciplinary approach to evaluate the relation between preterm birth, a common and well defined health outcome, and exposure to contamination from well-defined sources, pathways and receptors. The rate of preterm birth in Puerto Rico in 2008, the most recent year with available data, was 19.6% or nearly 1 out of every five births. Puerto Rico has gradually experienced nearly a doubling in the preterm rate since 1990, when it was at just 11.4%. The usual causes of preterm births, such as lack of prenatal care in the first trimester, maternal education, maternal smoking in pregnancy, and increased use of assisted reproductive technology (ART), do not explain the increase in the preterm rate observed in Puerto Rico. Through integrated analytical, mechanistic, epidemiology, fate-transport, and remediation studies, along with a centralized, indexed data repository, the program will deliver new knowledge and technology in the area of contaminants as a potential cause of preterm birth.

Development of a multi-scale packing methodology for evaluating fate and transport processes of explosive-related chemicals in clayey soils

The development of the scalable systems and methods involves proper reproduction of soil composition, lithology and structures, appropriate placement of boundary conditions, suitable simulation of representative environmental conditions, and the use of representative sampling systems. This paper evaluates the effect of different packing methods with a tropical sandy soil for obtaining a uniform and homogeneous packing so that these characteristics are comparable across all scales and dimensions. The packing methods used include piston-driven dry packing, piston-driven wet packing, and gravity-driven sedimentation packing. For dry and wet packing, the procedure consisted on the iterative addition of soil layers, mixing and compaction. Sedimentation packing involved the preparation of soil slurry and allowing its deposition under gravity. The systems were evaluated for consistent bulk density, porosity, homogeneity, and soil dispersivity. Preliminary results exhibit satisfactory bulk density and porosity values for the piston-driven methods, ranging from 1.59 to 1.64 g cm-3 and from 42 to 44%, respectively. Sedimentation packing results in fair homogeneity and gradation, while dry packing develops heterogeneous layering. Transport parameters were also evaluated resulting in consistent dispersivity values for wet piston-driven packing ranging from 0.09-0.19 cm. Wet piston-driven packing is recommended as they yielded the most reproducible results for tropical sandy soils. The reproducibility of the recommended method is tested and proven in other physical models of different scales and dimensions. The method herein developed are, therefore, applicable for the development of representative multidimensional physical models designed to simulate soil and environmental fate and transport processes occurring in field conditions where landmines and other explosive devices are present.