Wildland-urban interface wildfire increases metal contributions to stormwater runoff in Paradise, California.

The 2018 Camp Fire was a large late-year (November) wildfire that produced an urban firestorm in the Town of Paradise, California, USA, and destroyed more than 18 000 structures. Runoff from burned wildland areas is known to contain ash, which can transport contaminants including metals into nearby watersheds. However, due to historically infrequent occurrences, the effect of wildland-urban interface (WUI) fires, such as the Camp Fire, on surface water quality has not been well-characterized. Therefore, this study investigated the effects of widespread urban burning on surface water quality in major watersheds of the Camp Fire area. Between November 2018 and May 2019, 140 surface water samples were collected, including baseflow and stormflow, from burned and unburned watersheds with varying extent of urban development. Samples were analyzed for total and filter-passing metals, dissolved organic carbon, major anions, and total suspended solids. Ash and debris from the Camp Fire contributed metals to downstream watersheds via runoff throughout the storm season. Increases in concentration up to 200-fold were found for metals Cr, Cu, Ni, Pb, and Zn in burned watersheds compared to pre-fire values. Total concentrations of Al, Cd, Cu, Pb, and Zn exceeded EPA aquatic habitat acute criteria by up to 16-fold for up to five months after the fire. To assess possible transport mechanisms and bioavailability, a subset of 18 samples was analyzed using four filters with nominal pore sizes ranging from 0.22 to 1.2 µm to determine the particulate size distribution of metals. Trace and major metals (Al, Ba, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn) were found mostly associated with larger grain sizes (>0.45 µm), and some metals (Al, Cr, Fe, and Pb) also included a substantial colloidal phase (0.22 to 0.45 µm). This study suggests that fires in the wildland-urban interface increase metal concentrations, mainly through particulate driven transport. The metals with the largest increases are likely from anthropogenic disaster materials, though biomass ash also is a major contributor to water quality. The increase in metals following WUI burning may have adverse ecological impacts.

Water-soluble organic carbon release from mineral soils and sediments in an irrigated agricultural system.

Water interactions with soil and vegetation are greatly altered in agricultural watersheds compared to natural landscapes, which impacts sources and fates of organic carbon (OC). While mineral soil horizons in natural ecosystems primarily act as filters for dissolved organic carbon (DOC) leached from organic surface horizons, tilled soils largely lack an organic horizon and their mineral horizons therefore act as a source for both DOC and sediment to surface waters. Irrigated watersheds highlight this difference, as DOC and total suspended sediment (TSS) concentrations simultaneously increase during the low-discharge irrigation season, suggesting that sediment-associated OC may constitute a significant source of DOC. While water-soluble OC (WSOC) from sediments and soils has been found to be compositionally similar to stream DOC, these contributions remain poorly quantified in agricultural streams. To address this, we conducted abiotic solubilization experiments using sediments (suspended and bed) and soils from an irrigated agricultural watershed in northern California, USA. Sediments (R2 > 0.99) and soils (0.74 < R2 < 0.89) displayed linear solubilization behaviors over the range of concentrations tested. Suspended sediment from the irrigation season exhibited the largest solubilization efficiency (10.9 ± 1.6% TOCsediment solubilized) and potential (1.79 ± 0.26 mg WSOC g-1 dry sediment), followed by suspended sediment from a winter storm, then bed sediment and soils. Successive solubilization experiments increased the total release of WSOC by ∼50%, but most (88-97%) of the solid-phase OC remained insoluble in water. Using these solubilization potential estimates and measured TSS concentrations, we estimated that WSOC from suspended sediment in streams represented 4-7% of the annual DOC export from the watershed. However, field sediment export is much higher than what is represented by suspended sediment in the water column, therefore field-scale contributions from sediments could be much higher than estimated.

Wildland-urban interface fire ashes as a major source of incidental nanomaterials.

Although metal and metalloid concentrations in wildfire ashes have been documented, the nature and concentrations of incidental nanomaterials (INMs) in wildland-urban interface (WUI) fire ashes have received considerably less attention. In this study, the total metal and metalloid concentrations of 57 vegetation, structural, and vehicle ashes and underlying soils collected at the WUI following the 2020 fire season in northern California - North Complex Fire and LNU Lightning Complex Fire - were determined using inductively coupled plasma-time of flight-mass spectrometry after microwave-assisted acid digestion. The concentrations of Ti, Zn, Cu, Ni, Pb, Sn, Sb, Co, Bi, Cr, Ba, As, Rb, and W are generally higher in structural/vehicle-derived ashes than in vegetation-derived ashes and soils. The concentrations of Ca, Sr, Rb, and Ag increased with increased combustion completeness (e.g., black ash < gray ash < white ash), whereas those of C, N, Zn, Pb, and In decreased with increased combustion completeness. The concentration of anthropogenic Ti - determined by mass balance calculations and shifts in Ti/Nb above the natural background ratios - was highest in vehicle ash (median: 30.8 g kg-1, range: 4.5-41.0 g kg-1) followed by structural ash (median: 5.5 g kg-1, range: of 0-77.4 g kg-1). Various types of carbonaceous INM (e.g., amorphous carbon, turbostratic-like carbon, and carbon associated with zinc oxides) and metal-bearing INMs (e.g., Ti, Cu, Fe, Zn, Mn, Pb, and Cr) with sizes between few nanometers to few hundreds of nanometers were evidenced in ashes using transmission electron microscopy, including energy dispersive X-ray spectroscopy. Overall, this study demonstrates the abundance of a variety of metals and metalloids in the form of INMs in WUI fire ashes. This study also highlights the need for further research into the formation, transformation, reactivity, fate, and effects of INMs during and following fires at the WUI.

Cell-free biosensors for rapid detection of water contaminants.

Lack of access to safe drinking water is a global problem, and methods to reliably and easily detect contaminants could be transformative. We report the development of a cell-free in vitro transcription system that uses RNA Output Sensors Activated by Ligand Induction (ROSALIND) to detect contaminants in water. A combination of highly processive RNA polymerases, allosteric protein transcription factors and synthetic DNA transcription templates regulates the synthesis of a fluorescence-activating RNA aptamer. The presence of a target contaminant induces the transcription of the aptamer, and a fluorescent signal is produced. We apply ROSALIND to detect a range of water contaminants, including antibiotics, small molecules and metals. We also show that adding RNA circuitry can invert responses, reduce crosstalk and improve sensitivity without protein engineering. The ROSALIND system can be freeze-dried for easy storage and distribution, and we apply it in the field to test municipal water supplies, demonstrating its potential use for monitoring water quality.