Equilibrium Environmental Inc. New Tier 1 Boron Guideline for Alberta Greg Huber, M.Sc., P.Eng., PMP (Equilibrium) Anthony Knafla, M.Sc., DABT (Equilibrium) Ian McIvor, M.Sc., P.Biol (Equilibrium) Holly Kingston, M.Sc., P.Geo (Equilibrium) Darlene Lintott, M.Sc. (Exova) Federal Contaminated Sites National Workshop Montreal, Quebec, April 25 th – 27 th 2016
Acknowledgements • Exova • Petroleum Technology Alliance of Canada (PTAC) • PTAC Boron Working Group • Environment Canada • Alberta Environment and Parks 2
Presentation Overview • Background and Existing Guidelines • Boron Adsorption and K d Values • Guideline Derivation for Soil Dependent Biota • Livestock and Wildlife Toxicity • Groundwater Pathways and Guidelines • Other Soil Pathways and Guidelines • Summary of Updated Tier 1 Soil Boron Guidelines 3
Background • Boron (B) a trace metalloid, typically as boric acid or borate salts • Natural sources: – Weathering of parent rock/minerals – Decay of plant material • Anthropogenic sources: – Produced water (often present with salts) e.g., oil and gas activities – Industrial sources (eg, boric acid, borax) e.g., fibreglass manufacturing – Agricultural sources (eg, fertilizer) • Essential micro-nutrient for plant growth – narrow range between deficiency and toxicity – levels too low can impair growth and yield – can be toxic at elevated levels • Plant B toxicity has been studied since 1930’s – excessive B can cause necrosis, yellowing, burning → – yield can be reduced at high B levels • Boron can also be toxic to various insects – borax and boric acid used as insecticides to control ants, termites, etc → 4
Background (cont’d) • At excessive levels, boron also a reproductive toxin to humans and animals • Humans consume some boron from food, and may also be occupationally exposed (eg, miners, factory workers) – Grazing animals (eg. cattle, sheep) may be exposed to boron in drinking water, or to boron bioconcentrated from soil into consumed vegetation – Mallards have been observed in California exposed to high boron levels in surface waters in irrigated regions with high natural boron California – ‘Red Rock Ranch’ showing residual salts including selenium and boron 5 Image from: ‘http://californiaagriculture.ucanr.org/landingpage.cfm?Article=ca.v063 n01p 41&fulltext=yes’
Existing guidelines and issues • Current CCME guideline of 2 mg/kg HWS (‘hot water soluble’) boron an ‘interim’ guideline from 1991 based on professional judgment – Alberta Tier 1 guideline was also 2 mg/kg HWS until this year • HWS test originally designed to evaluate deficiency, not toxicity • Background concentrations may exceed guideline in some soils – background up to 3-13 mg/kg in clayey or organic soils in Alberta • Good plant growth has been observed in the field and lab at levels above the current Tier 1 guideline – e.g, 4-10 mg/kg HWS or higher for typical soils • HWS boron highly dependent on soil texture and sorption properties • Other test methods (eg, saturated paste boron) may be more useful – potentially better correlation with plant toxicity over a range of soil textures – relevant to groundwater transport and groundwater pathways on a mg/L basis • Relationships between HWS and saturated paste boron useful for comparing old data with new data – also relevant to soil sorption behavior and K d values 6
Boron Adsorption and K d Values 7
Boron Adsorption in Soil – K d Aspects • K d (distribution coefficient) is related to partitioning of boron between soil and pore water (soil solution) • Soils with high clay content or organic matter content have greater surface area and thus higher sorptive ability – Adsorption is thus correlated to soil texture • Sorption is commonly explored via a distribution coefficient, K d which is defined as: K d = adsorbed boron (mg/kg) Example dissolved boron (mg/L) dataset K d can be estimated from slope: HWS B (mg/kg) = K d + Sat% sat paste B (mg/L) 100 8
Boron Adsorption in Soil – K d Aspect • Used this technique for over 2,300 data points from over 40 sites across Alberta spanning a range of soil textures • K d correlated to texture via saturation percentage (sat % a proxy for texture, see Equilibrium 2014 PTAC presentation) ZOOMED IN 10 9 8 7 6 HWS ¡B ¡(mg/kg) 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 10 9 sat ¡paste ¡B ¡(mg/L) <43% 43-‑100% >100%
Guideline Derivation for Soil Dependent Biota 10
Plant toxicity testing • Recent toxicity studies carried out by Exova (Edmonton lab) on agricultural and boreal plant species • Example responses and 25% effect levels shown below 150 White spruce 125 100 % of control 75 50 25 0 0.0 0.1 1.0 10.0 100.0 1000.0 Saturated paste boron (mg/L) SL-organic RL-organic SB-organic 11 RB-organic SL-artificial RL-artificial SB-artificial RB-artificial SL-mineral RL-mineral SB-mineral RB-mineral
Plant Toxicity Testing Durum Wheat Alfalfa Jack Pine Carrot Northern Wheatgrass 12 Darlene.Lintott@exova.com
Plant toxicity testing: • Boron concentrations across soil textures are less variable when expressed as saturated paste B More consistent response by texture with sat paste boron 13
Soil Dependent Biota – Plants (literature) • Toxicity research in California by Eaton (1944) on various fruit, vegetable and grass/grain species in sand cultures irrigated with boron at 0, 1, 5, 10, 15 mg/L. • Visual effects and changes in biomass recorded • IC 25 ’s estimated for cases where clear dose-response observed Examples • More recent sand culture experiments carried out on additional food- crops (broccoli, squash, tomato, etc), and to refine threshold levels from the 1944 results • Slopes and thresholds useful for estimating 25% effect levels (IC 25 ’s) 14
Soil Dependent Biota – Soil Invertebrates • Various Environment Canada (and related) studies from 2004 - 2012 - Soil invertebrates such as earthworms, springtails and mites are important receptors in soil, along with plants - Boric acid used as toxicant - Tests conducted in artificial and field soils - Acute avoidance, lethality, and reproduction used as end points Earthworm Springtail Oribatid mite 15
Soil Dependent Biota – Soil Invertebrates • Recent Exova research in combination with toxicity data from published literature and method development studies was combined to derive IC 25 ’s across species and soil types – Substantial work done by Environment Canada, Method Development Unit • Reproductive endpoints used to derive IC 25 ’s are shown below as an example of the invertebrate dataset • In many cases sat paste boron estimated from spiked levels and regressions. For Exova tests, sat paste B measured directly 16
Guideline to Protect Soil Dependent Biota • Direct eco-contact guideline derived based on the ranked IC 25 s for all soil dependent biota which includes: - Agricultural plants (crops, grasses, trees, fruits, vegetables) -Boreal plants (trees, grasses, other plants) -Soil invertebrates (earthworms, mites, springtails) • Coarse and fine grained soil generally combined since similar responses on sat paste B basis • The IC 25 s for soil dependent biota were plotted in a species sensitivity distribution (SSD). Guidelines determined from best fit to toxicity data SSD (log-linear distribution) Direct eco-contact guideline Agricultural (25 th percentile) 3.3 mg/L sat paste B Commercial/Industrial (50 th percentile) 7.9 mg/L sat paste B • Note that these soil guidelines are on a mg/L saturated paste basis rather than the more typical mg/kg basis 17 -Consistent with salinity, which measures conductivity in saturated paste
Soil Dependent Biota -Combined Ranked IC 25 s Species Sensitivity Distribution (SSD) 18
Livestock and Wildlife Toxicity 19
Livestock and Wildlife Soil & Food Ingestion • Grazing animals may be exposed to elevated boron and other metals which have accumulated from soil into consumed vegetation • Boron is less toxic to grazers than some other metals such as molybdenum and selenium, but in some cases naturally occurring boron can be ingested at potentially toxic levels. • Toxicity data from literature reviewed for rats, mice, cattle, chickens, mallards, rabbits, etc • Variability of data between the studies poses challenges in deriving IC 25 s • Thus, a guideline for protection of livestock and wildlife soil and food ingestion is not explicitly derived, rather exposures and risks have been evaluated for typical species assuming soils at the direct eco- contact guideline for plants/invertebrates 20
Bioconcentration into Plants • B uptake into plants described by ‘bioconcentration factors’ (BCF’s) • Estimated daily exposures to B calculated from soil at 3.3 mg/L sat paste using vegetation BCF’s BCF = vegetation boron (mg/kg) / soil boron (mg/kg HWS boron) • BCF’s vary with soil texture if using HWS B. Differences become less if using sat paste B (mg/L) instead, but BCF’s typically calculated on mg/kg basis and thus retained here • Average BCF (roots and shoots combined) is 17.4 for coarse soil and 9.7 for fine soil, consistent with other AB field and tub studies 21
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