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Several areas in Hawaii have background concentrations of unexploded ordnance (UXO) as a consequence of past and current military training. The presence of UXO and the release of their chemical compounds can be of environmental concern. The complete and incomplete detonation of explosives can ignite vegetation fires that cause organics in the topsoil to burn, and therefore, impact the environmental fate of these compounds. The sorption and transport of two UXOs, HMX and RDX, were investigated in a surface soil that was previously exposed to a fire event. In addition, a control soil that had not been exposed to a fire event was used. The use of burned and unburned soil to simulate soil that has been directly impacted by the explosion of UXOs combined with the uniqueness of the soil properties in Hawaii represents the novelty of this study. The surface soil that had been previously exposed to a fire event showed greater adsorption than the control, which was possibly due to a reduction of macropores in the burned soil and the presence of fine charcoal particles. Regardless of the presence or absence of a fire event, HMX showed a greater sorption affinity than RDX. [ABSTRACT FROM AUTHOR]

BACKGROUND: Physically based tier-II models may serve as possible alternatives to expensive field and laboratory leaching experiments required for pesticide approval and registration. The objective of this study was to predict pesticide fate and transport at five different sites in Hawaii using data from an earlier field leaching experiment and a one-dimensional tier-II model. As the predicted concentration profiles of pesticides did not provide close agreement with data, inverse modeling was used to obtain adequate reactive transport parameters. The estimated transport parameters of pesticides were also utilized in a tier-I model, which is currently used by the state authorities to evaluate the relative leaching potential. RESULTS: Water flow in soil profiles was simulated by the tier-II model with acceptable accuracy at all experimental sites. The observed concentration profiles and center of mass depths predicted by the tier-II simulations based on optimized transport parameters provided better agreements than did the non-optimized parameters. With optimized parameters, the tier-I model also delivered results consistent with observed pesticide center of mass depths. CONCLUSION: Tier-II numerical modeling helped to identify relevant transport processes in field leaching of pesticides. The process-based modeling of water flow and pesticide transport, coupled with the inverse procedure, can contribute significantly to the evaluation of chemical leaching in Hawaii soils. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The article discusses the result of the field and laboratory experiments in five sites in Hawaii for ground leaching of pesticides including bromide, atrazine, and triflozystrobin. It focuses on the impact of the duration and sorption of chemicals on the drinking source groundwater. The experiment with Hawaii Department of Agriculture (HDOA) resulted to the sorption of all chemicals and its presence in the water, except for trifloxystrobin which is the most mobile compound.

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A simulation of the transport of dibromochloropropane (DBCP) and ethylene dibromide (EDB) in the vadose zone and ground water was conducted in the Mililani area of central Oahu, Hawaii to revisit the ground water contamination predictions made by researchers at the University of Hawaii in 1988 for selected wells of the Honolulu Board of Water Supply. Examination of sampled DBCP results in these wells indicated a large discrepancy between the observed and predicted concentrations in 1988. Therefore, a postaudit study was initiated in the same area to assist in better defining projected concentrations of contaminants in well waters in the future. With the new data, different modeling approaches were undertaken for simulating flow and contaminant transport in both the vadose and saturated zones. The new simulations indicate travel times of 14–32 years for contaminants to reach the water table, depending on the location. The approximate recovery time of wells in the study area is expected to occur after the year 2016 for DBCP. The predicted concentration of EDB in the wells is less than the current detection limit. Variabilities in model predictions due to parameter uncertainties and model limitations are also considered. Although the predicted concentrations from the present simulations match sampled data better than the concentrations from earlier modeling efforts, still a number of uncertainties remain. [ABSTRACT FROM AUTHOR]

The anticoagulant rodenticides brodifacoum, chlorophacinone, and diphacinone have been proposed for broadcast application in some forested areas in Hawai'i to protect rare and endangered native bird species from introduced mice and rats. Groundwater resources in Hawai'i are prone to contamination due to the intrinsic aquifer vulnerability to leaching from the land surface. Because of the hydrogeologic complexity, Hawai'i uses a Tier-I leaching assessment tool, CLERS, to make registration decisions for new or existing chemicals. The CLERS tool uses soil and pesticide properties as well as water recharge through the soil profile in a GIS framework to estimate mass attenuation of the chemicals at a given depth and compares against this attenuation factor against those of a known leacher and a non-leacher. Disturbed soil samples were collected across the state of Hawai'i, including the islands of Hawai'i, Kaho'olawe, Kaua'i, Lana'i, Maui, Moloka'i, and O'ahu, with two sampling locations per island, except for Kaua'i which had three. As only limited information on chemical properties of these anticoagulants in soils is available, laboratory experiments were performed to determine the sorption capacity (K d ) and the degradation rate (T 1/2 ) of brodifacoum, chlorophacinone, and diphacinone to construct a proper chemical database. Depending on the soil type, T 1/2 values ranged between 37 and 248 days for diphacinone, between 39 and 1000 days for chlorophacinone, and between 72 and 462 days for brodifacoum. These data were used in the CLERS tool to estimate leaching risks for these chemicals primarily in forested areas of the state where the chemicals are likely to be applied. The results from the CLERS tool indicate low risks of leaching of these three compounds into aquifers in five out of six major Hawaiian Islands. Diphacinone showed medium risk of leaching in a few remote areas in Maui. [ABSTRACT FROM AUTHOR]

Abstract: Arsenical herbicides were used extensively for emergent weed control in Hawaiian sugar cane cultivation from 1913 to about 1950. As a result, surface soil arsenic concentrations average 280mgkg−1 across more than 60km2 of former sugar plantation land in the eastern portion of the Island of Hawaii. This study was conducted to elucidate the relationship between soil properties and arsenic bioaccessibility in the iron-rich volcanic soils. Soils are predominantly Andisols, formed by weathering of basaltic lava and tephra, with pedogenic solid phases consisting of short-range order iron oxyhydroxides, allophane-like aluminosilicates, and metal-humus compounds. These reactive solid phases strongly adsorb oxyanions, such as phosphate and arsenite/arsenate. High arsenic sorption capacity limits desorption and vertical migration within the soil column and prevents contamination of the underlying groundwater aquifer, despite high arsenic loading and precipitation rates. In vitro arsenic bioaccessibility, as measured by the SBRC gastric-phase test, ranges from 2% to 35% and averages 9% of total arsenic. Bioaccessible arsenic is higher in less weathered soils (Udifolists, Typic and Lithic Hydrudands) and lower in more weathered ash-dominant soils (Acrudoxic Hydrudands). Soil weathering indicators, such as reactive iron content, are strong predictors of arsenic bioaccessibility. Based on evidence from soil mineralogy, geochemistry and arsenic speciation, as well as limited soil arsenic bioavailability/bioaccessibility comparisons, risks to human health from direct contact (soil ingestion) are significantly reduced by low arsenic bioaccessibility. Nonetheless, some soils within former sugar cane cultivation areas contain bioaccessible arsenic concentrations exceeding Hawaii Department of Health risk-based action levels, and will require mitigating actions. Even higher levels of soil arsenic contamination have been identified at former pesticide storage and mixing areas, but are generally of localized extent. [Copyright &y& Elsevier]

Abstract: The adsorption and degradation behavior of RDX, HMX, TNT and DNT and the impact of pH, ionic strength and dissolved organic matter on sorption were examined for two volcanic soils of a former military training area on Hawaii Island, Hawaii, USA. The transport of these chemicals in the soil was also studied in small packed columns and simulated using a water-flow and solute-transport model, HYDRUS_1D. The results show that HMX and RDX are both significantly more mobile than TNT and DNT. The adsorbability of the four chemicals was ranked as: RDXRDX>DNT>TNT. No significant trend was observed for the effect of ionic strength, pH and dissolved organic carbon (DOC) on the adsorption of explosive compounds within the concentrations and pH ranges evaluated. The simulation results show that TNT and DNT would not leach beyond a depth of 30cm soil profile whereas a significant amount of HMX and RDX would pass the 30cm depth. It seems that the risk for contamination of groundwater is much higher for both HMX and RDX than for DNT and TNT as the substratum in this area consists of highly permeable lavas. [ABSTRACT FROM AUTHOR]

The fate of pesticides in tropical soils is still not understood as well as it is for soils in temperate regions. In this study, water flow and transport of bromide tracer and five pesticides (atrazine, imazaquin, sulfometuron methyl, S-metolachlor, and imidacloprid) through an undisturbed soil column of tropical Oxisol were analyzed using a one-dimensional numerical model. The numerical model is based on Richards' equation for solving water flow, and the advection-dispersion equation for solving solute transport. Data from a laboratory column leaching experiment were used in the uncertainty analysis using a global optimization methodology to evaluate the model's sensitivity to transport parameters. All pesticides were found to be relatively mobile (sorption distribution coefficients lower than 2 cm(3) g(-1)). Experimental data indicated significant non-conservative behavior of bromide tracer. All pesticides, with the exception of imidacloprid, were found less persistent (degradation half-lives smaller than 45 days). Three of the five pesticides (atrazine, sulfometuron methyl, and S-metolachlor) were better described by the linear kinetic sorption model, while the breakthrough curves of imazaquin and imidacloprid were more appropriately approximated using nonlinear instantaneous sorption. Sensitivity analysis suggested that the model is most sensitive to sorption distribution coefficient. The prediction limits contained most of the measured points of the experimental breakthrough curves, indicating adequate model concept and model structure for the description of transport processes in the soil column under study. Uncertainty analysis using a physically-based Monte Carlo modeling of pesticide fate and transport provides useful information for the evaluation of chemical leaching in Hawaii soils., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Former sugarcane lands on the Island of Hawaii have elevated levels of soil arsenic (As) from historical use of arsenical pesticides. The bioaccessible fraction of total As (AsTOT), a measure of the potential for human As uptake by incidental ingestion of soil, is used in the assessment of human health risk and the determination of the need for remedial action. Ferric chloride plus lime and ferrous sulfate plus lime were applied to As-contaminated soils in a field plot setting to determine the potential for reducing in vitro bioaccessible As (AsIVBA) by increasing As sequestration by the formation of additional iron (Fe) oxyhydroxides. The two Fe sources performed similarly in reducing AsIVBA over a 2-year observation period, with 30-41% reduction in AsIVBA for 0.25wt% Fe dosing (dry soil basis) and 59-63% reduction for 0.5wt% Fe dosing. Addition of phosphate (PO4) to treated and untreated soils caused a significant increase in AsIVBA. Iron-treated and control soils showed more than twice the AsIVBA after the addition of 1500mgPkg(-1). The cost of in situ treatment of As-contaminated soil with ferrous sulfate plus lime to lower AsIVBA was estimated to be an order of magnitude less than excavation and landfill disposal on the Island of Hawaii, making the technology a viable alternative when remedial action objectives were based on AsIVBA levels., (Copyright © 2014 Elsevier B.V. All rights reserved.)

We examined the mobility of 2-amino-4,6-dinitrobenzoic acid (2-A-4,6-DBA) a common photodegradation product of TNT, in soil taken from a former military training area on Oahu Island, Hawaii, USA. 2-A-4,6-DBA is stable and polar and has the potential to migrate to groundwater. Little experimentation has been conducted on explosives in tropical soils which differ chemically from soils in temperate climates. 2,4,6-Trinitrotoluene (TNT) and 1,3,5-hexahydro-1,3,5-trinitrotriazine (RDX) are the most commonly used secondary military explosives. Composition B (Comp B) is a frequently used 59/40/1 combination of RDX, TNT, and wax binder. In order to examine the effect of the presence of Comp B and its degradation products on the mobility of 2-A-4,6-DBA in soil, we dissolved field-collected Comp B fragments in water, exposed the solution to light and pumped it through soil and sand-packed stainless steel columns under abiotic saturated conditions. We found that in the presence of a complex mixture of explosives and degradation products, 2-A-4,6-DBA migrated faster than the parent compound (TNT) and other degradation products through both tropical soil and Ottawa sand (used as a reference) under sterile saturated conditions. The relatively rapid movement of 2-A-4,6-DBA suggests that it has the potential to contaminate underlying groundwater. However, the amount of 2-A-4,6-DBA produced under field conditions and its rate of biotic degradation were not part of this research, therefore, it is unknown how these factors might affect the transport and fate of 2-A-4,6-DBA., (Copyright © 2013 Elsevier B.V. All rights reserved.)