Abstract
Despite a declining trend, California remains a significant oil-producing state. For every barrel of crude oil, an average of 15 barrels of oilfield produced water (OPW) is generated, some of which is used to boost freshwater sources for crop irrigation in the agriculturally important Central Valley. OPW is known to contain salts, metals, hydrocarbons, alkylphenols, naturally radioactive materials, biocides, and other compounds from drilling and production processes. Less is known about the potential uptake and accumulation of these compounds in crops and soil irrigated with OPW. In this study, 23 potted mandarin orange plants were irrigated two to three times weekly (depending on season) with water containing three different concentrations of the known OPW heavy metals barium, chromium, lead, and silver. Seven sets of samples of soil and leaves and 11 fruits were collected and processed using microwave-assisted digestion (EPA Method 3051A). Processed samples were analyzed using inductively coupled plasma-optical emission spectroscopy (ICP-OES). Analysis of variance (ANOVA) and covariance (ANCOVA) coupled with Tukey’s honest significant difference test were used to examine the effects of metal concentrations in the irrigation water and number of watering days, respectively, on the metal concentrations in the soil, leaf, and fruit samples. Accumulation of barium in soil and leaves was strongly positively associated with sample and number of watering days, increasing nearly 2000-fold. Lead also showed an upward trend, increasing up to 560-fold over the baseline level. Total chromium showed an increase in the soil that tapered off, but less consistent results in the leaves and fruit. The silver results were more volatile, but also indicated at least some level of accumulation in the tested media. The smallest absolute accumulation was observed for chromium. Concentrations in the fruit were highest in the peel, followed by pith and juice. Accumulation of all heavy metals was generally highest in the soil and plants that received the highest irrigation water concentration. Considering the potential for adverse human health effects associated with ingesting soluble barium contained in food and drinking water, and to a lesser extent chromium and lead, the study signals that it is important to conduct further research into the accessibility and bioavailability of the tested heavy metals in the soil and whether they pose risks to consumers.
Highlights
California is still the third-largest oil-producing state in the United States [1]
oilfield produced water (OPW) is high in salts and dissolved solids and may contain metals, alkylphenols, trace elements, hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), benzene, toluene, ethylbenzene, and xylenes, naturally occurring radioactive materials (NORMs), biocides, and other compounds used during the production process [3]
Ttlhyefosutunddyi’ns sgiomaillsarwceornecteontdraettieocnt sthine osoilifilealnddprpoldanutce(ldeawvaetse,rf(rOuiPt)Wc)o,nacnednttoraetxioanmsinofe tihf ethseereelwemereendtse,tewcthaibclhe tarreendfrseoqvueernttilmy efoaunnddasina fsuimncitliaorncoofntcheenmtreattaiolsn’scoinncoeniltfriaeltdionprinodthueceirdrigwaatitoenr,Inanthdetaobesexnacmeionfefiefdtehrearle(awndersetadteet)ercetgaublleatitorennsdosnotvheerpteimrmeisasnibdleascoancfuenntcrtaiotinonosf otfhtehmeseetaanlsd’ cootnhceernctoramtipoonunindsthfoeuinrdriginatOioPnWw, aitteirs.oIfninttheeresatbtsoenlecearnofabfeoduetrtahl e(iarnfadtestwathee)nrOegPuWlatiisonresuosendtfhoer permissible concentrations of these and other compounds found in OPW, it is of interest to learn about their fate when OPW is reused for agricultural crop irrigation on a frequent basis, as is the case in several water districts in California’s agriculturally important Central Valley
Summary
California is still the third-largest oil-producing state in the United States [1]. During the oil production process, substantial volumes of oilfield produced water (OPW, referred to as oilfield brine, connate water, or formation water) are typically generated, especially as the well and oilfield matures. OPW is the largest waste stream by volume in the exploration and extraction of oil, and over the lifespan of an oilfield the total volume of produced water can exceed tenfold the volume of hydrocarbons produced [3]. OPW is high in salts and dissolved solids and may contain metals, alkylphenols, trace elements, hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), benzene, toluene, ethylbenzene, and xylenes (collectively known as BTEX), naturally occurring radioactive materials (NORMs), biocides, and other compounds used during the production process [3]. Oil and gas production wastewater: Soil contamination and pollution prevention.
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