Recipient Organization
UNIV OF HAWAII
3190 MAILE WAY
HONOLULU,HI 96822
Performing Department
(N/A)
Non Technical Summary
The Maui wildfires on August 8, 2023 caused the largest wildfire-related human fatality in the modern U.S. history, in addition to significant properties destruction and long-lasting environmental damages in several coastal and upcountry communities. For the agricultural and forest areas impacted by the wildfires, one major knowledge gap is whether chromium (VI) (Cr(VI)) would become a major or even dominant public health risk diver in the immediate aftermath of the disaster and during the long-term recovery and rebuilding processes. Because the volcanic Hawaii soils contain extraordinarily high levels of total Cr, the overarching hypothesis of the project is that the soil Cr can be transformed to Cr(VI) through thermochemical oxidation. Because Cr(VI) is high toxic and mobile, it can affect public health in agricultural communities through multiple exposure routes, including direct skin contact, dust inhalation, and drinking water consumption. The goal of this project is to understand the abundance and fate of Cr(VI) in the Maui wildfire-impacted soil, and to develop cost-effective and practical bioremediation strategies. To achieve this goal, the first objective will determine the impact of Maui wildfires on the speciation of total Cr in agricultural and forest soils through field sampling and laboratory experiments, and the second objective will conduct laboratory experiments to test mulching and acidic compost amendment as cost-effective and practical bioremediation strategies to reduce soil Cr(VI). The project results will include field sampling and laboratory experimental data on the abundance and fate of Cr(VI) in the Maui wildfire-impacted soil samples and in soil samples subjected to the bioremediation strategies. The anticipated impact is improved understanding of the wildfires' impact on Cr(VI) in the agricultural and forestry soil environments, development of bioremediation strategies, and extension and education to communicate associated public health risks to the impacted communities.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
The Maui wildfires on August 8, 2023 caused the largest wildfire-related human fatality in the modern U.S. history, in addition to significant properties damages and environmental degradation in several coastal and upcountry communities. In the immediate aftermath and during the long-term recovery and rebuilding processes, it is imperative to understand and mitigate the wildfires' impact on agricultural land and forest soil environments in order to enhance agroecosystems resilience and protect health, well-being and safety of the communities. The volcanic Hawaii soils contain extraordinarily high levels of total chromium (Cr), which may be oxidized to the high toxic Cr(VI) that can affect human health through multiple exposure routes. The goal of this project is to address this important knowledge gap on whether chromium (Cr) would become a major or even dominant risk diver and to develop bioremediation strategies.Objective 1. Determine the impact of Maui wildfires on the speciation of Cr in agricultural and forest soils. The working hypothesis is that the Maui wildfires oxidized Cr(III) to Cr(VI) through thermochemical oxidation in surface soils. To test the working hypothesis, the project will both conduct field sampling at the agricultural and forest sites impacted by the Maui wildfires and conduct laboratory experiments for confirmation and to further mechanistic understanding. The extension components of this objective will include risk communication to impacted communities through responsible government agencies, outreach information brochures, social media posts, community meetings, and academic seminars/webinars. The education component will involve development of course materials to increase exposure to undergraduate and graduate students.Objective 2. Test soil mulching and acidic compost amendment as two bioremediation strategies to mitigate Cr(VI) in Maui wildfire-impacted soils. The lack of reducing agents (e.g. soil organic matters) and the high pH values in wildfire-impacted soils are conditions that enable Cr(VI) to have a long half-life in Maui wildfire-impacted soil. To reduce health risks from Cr(VI), it is imperative to develop and test cost-effective and practical bioremediation strategies to detoxify Cr(VI) in soil. The working hypothesis is that chemical and microbial Cr(VI) reduction can be rapidly achieved through soil mulching or acidic compost amendment. This objective will include laboratory tests to determine and compare the effectiveness of the two strategies, and extension efforts to encourage and facilitate the better performing strategy at pilot sites in Maui wildfire-impacted agricultural and forest soils.
Project Methods
Methods for Objective 1.To test the working hypothesis, the project will both conduct field sampling at the agricultural and forest sites impacted by Maui wildfires and conduct laboratory experiments for confirmation and to further mechanistic understanding (Table 1). Soil core samples (500 cm) will be collected from a total of ten wildfire-impacted sites, five from impacted agricultural land upwind and upslope of Lahaina and five from forest sites near Upcountry and Kula, Maui. Soil core samples will also be collected from four non-impacted sites as controls, two from Lahaina area and two from the Upcountry/Kula areas. The soil core sample will be divided into four subsamples based on soil depths (0-20 cm, 20-100 cm, 100-300 cm, and 300-500 cm), and two aliquots of each subsample will be processed and analyzed as analytical duplicates. The soil samples will be subjected to chemical analyses to quantify total chromium, other heavy metals, and exchangeable Cr(VI). We will also conduct laboratory heating experiments to further confirm field sampling observations, and also to determine the temperature dependency of Cr oxidation in Maui soils. The laboratory heating experiment will follow the protocol previously described (17). Briefly, three different Maui soil samples not impacted by the wildfires (as experimental triplicates) will be heated in a muffle furnace at ambient atmosphere oxygen pressure and at four different temperatures. The experimental results from the different temperatures are designed to mimic different temperatures expected at different soil depths.The soil samples will be subjected to acid digestion per EPA Method 3050B for the extraction of total chromium and other heavy metals. The soil extracts will then be analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES) to quantify total chromium and other heavy metals. The method performance will be calibrated by testing duplicates of a NIST standard reference material. For Cr(VI), the soil samples will be subjected to alkali extraction per the modified EPA Method 3060A for Cr(VI) (20), and then analyzed by the 1,5-diphenylcarbazide (DPC) spectrophotometric method (17). If the primary chemical analytical methods outlined above failed to perform, alternative methods will be considered. An alternative method is the HPLC-DRC-ICP-MS, which can determine Cr(III), Cr(VI), As(III), As(V), Se(IV), and Se(VI) in a single analysis method (21). For Cr(VI) in soil, the soil samples may also be directly subjected to X-ray absorption near edge structure spectroscopy (XANES), which was previously shown to quantify Cr(VI) directly in the solid state (22). Concentrations of total chromium and Cr(VI) in the soil core samples from the ten wildfire-impacted agricultural and forest sites and the four unimpacted control sites will be compared to test the hypothesis. Statistical tests including ANOVA and Student's t test will conducted in the R environment. Statistically significant higher concentration or proportion of Cr(VI) in the wildfire-impacted soils than in the control soils, and significantly higher concentration or proportion of Cr(VI) in the surface and shallower soil than in the deeper soil would support the working hypothesis. Similarly, higher concentration or proportion of Cr(VI) in the heat treated Maui soil in the laboratory heating experiment would support the working hypothesis.Methods for Objective 2 The objective will conduct laboratory experiments to determine the effectiveness of two bioremediation strategies (organic mulching vs acidic compost amendment) in reducing Cr(VI) to Cr(III). The upper compartment of the laboratory batch reactors (Figure 3) will contain an agricultural soil sample that has been tested to contain elevated concentration of Cr(VI). The initial soil moisture level will be set at 60% of the total water holding capacity of the soil sample, which is designed to maximize aerobic microbial activities. The soil surface will be covered with organic mulch, acidic compost, or no addition (control); with all three treatments being conducted in triplicate reactors. All reactors will be aerated by passing air that is first bubbled through deionized water to increase humidity and thus maintain the overall soil moisture level through the course of the experiment. Although the design here is to simply cover the soil surface with organic mulch and acidic compost, with the assumption that the physical-chemical and microbial effects will quickly diffuse through the soil depth, mixing of the amendment materials, in particular acidic compost, can also be tested if the current design does not achieve the anticipated effects.All reactors will be sampled over time (Day 0, 1, 4, 7, 14, and 30), and the soil samples will be subjected to the chemical analyses described in Objective 1. At different time points, the total chromium and Cr(VI) concentration in the reactors will be compared amongst the three sets of reactors (ANOVA with post hoc tests) to determine if statistically significant lower Cr(VI) concentration is observed in the two sets of reactors that received mulch and organic compost than in the control reactors. The total chromium concentrations are expected to remain constant for all reactors over time, which will be used as a benchmark for analytical controls. The change of Cr(VI) concentration over time will be modeled with the 1st order reaction kinetic equation, and the rate coefficients will be compared through ANCOVA analysis. The bioremediation strategies with faster Cr(VI) decay coefficient will be identified as the more efficient bioremediation strategy. Additionally, the soil samples will also be analyzed for TOC/TN (for increased nutrient availability), and for total bacterial biomass through qPCR quantification of 16S rRNA gene. These data will be analyzed in conjunction with the Cr(VI) data to confirm the underlying remediation mechanisms.