Is Food Irrigated with Oilfield-Produced Water in the California Central Valley Safe to Eat? A Probabilistic Human Health Risk Assessment Evaluating Trace Metals Exposure.

Reuse of oilfield-produced water (OPW) for crop irrigation has the potential to make a critical difference in the water budgets of highly productive but drought-stressed agricultural watersheds. This is the first peer-reviewed study to evaluate how trace metals in OPW used to irrigate California crops may affect human health. We modeled and quantified risks associated with consuming foods irrigated with OPW using available concentration data. The probabilistic risk assessment simulated OPW metal concentrations, crop uptake, human exposures, and potential noncancer and carcinogenic health effects. Overall, our findings indicate that there is a low risk of ingesting toxic amounts of metals from the consumption of tree nuts, citrus, grapes, and root vegetables irrigated with low-saline OPW. Results show increased arsenic cancer risk (at 10-6 ) for adult vegetarians, assuming higher consumption of multiple foods irrigated with OPW that contain high arsenic concentrations. All other cancer risks are below levels of concern and all noncancer hazards are far below levels of concern. Arsenic risk concerns could be mitigated by practices such as blending high-arsenic OPW. Future risk assessment research should model the risks of organic compounds in OPW, as our study focused on inorganic compounds. Nevertheless, our findings indicate that low-saline OPW may provide a safe and sustainable alternative irrigation water source if water quality is adequately monitored and blended as needed prior to irrigation.

Novel trophic niches drive variable progress towards ecological speciation within an adaptive radiation of pupfishes.

Adaptive radiation is recognized by a rapid burst of phenotypic, ecological and species diversification. However, it is unknown whether different species within an adaptive radiation evolve reproductive isolation at different rates. We compared patterns of genetic differentiation between nascent species within an adaptive radiation of Cyprinodon pupfishes using genotyping by sequencing. Similar to classic adaptive radiations, this clade exhibits rapid morphological diversification rates and two species are novel trophic specialists, a scale-eater and hard-shelled prey specialist (durophage), yet the radiation is <10 000 years old. Both specialists and an abundant generalist species all coexist in the benthic zone of lakes on San Salvador Island, Bahamas. Based on 13 912 single-nucleotide polymorphisms (SNPs), we found consistent differences in genetic differentiation between each specialist species and the generalist across seven lakes. The scale-eater showed the greatest genetic differentiation and clustered by species across lakes, whereas durophage populations often clustered with sympatric generalist populations, consistent with parallel speciation across lakes. However, we found strong evidence of admixture between durophage populations in different lakes, supporting a single origin of this species and genome-wide introgression with sympatric generalist populations. We conclude that the scale-eater is further along the speciation-with-gene-flow continuum than the durophage and suggest that different adaptive landscapes underlying these two niche environments drive variable progress towards speciation within the same habitat. Our previous measurements of fitness surfaces in these lakes support this conclusion: the scale-eating fitness peak may be more distant than the durophage peak on the complex adaptive landscape driving adaptive radiation.

The impact of using low-saline oilfield produced water for irrigation on water and soil quality in California.

The consecutive occurrence of drought and reduction in natural water availability over the past several decades requires searching for alternative water sources for the agriculture sector in California. One alternative source to supplement natural waters is oilfield produced water (OPW) generated from oilfields adjacent to agricultural areas. For over 25 years, OPW has been blended with surface water and used for irrigation in the Cawelo Water District of Kern County, as permitted by California Water Board policy. This study aims to evaluate the potential environmental impact, soil quality, and crop health risks of this policy. We examined a large spectrum of salts, metals, radionuclides (226Ra and 228Ra), and dissolved organic carbon (DOC) in OPW, blended OPW used for irrigation, groundwater, and soils irrigated by the three different water sources. We found that all studied water quality parameters in the blended OPW were below current California irrigation quality guidelines. Yet, soils irrigated by blended OPW showed higher salts and boron relative to soils irrigated by groundwater, implying long-term salts and boron accumulation. We did not, however, find systematic differences in 226Ra and 228Ra activities and DOC in soils irrigated by blended or unblended OPW relative to groundwater-irrigated soils. Based on a comparison of measured parameters, we conclude that the blended low-saline OPW used in the Cawelo Water District of California is of comparable quality to the local groundwater in the region. Nonetheless, the salt and boron soil accumulation can pose long-term risks to soil sodification, groundwater salinization, and plant health; as such, the use of low-saline OPW for irrigation use in California will require continual blending with fresh water and planting of boron-tolerant crops to avoid boron toxicity.