New Tier 1 Boron Guideline for Alberta Greg Huber, M.Sc., P.Eng., - - PowerPoint PPT Presentation

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 25th – 27th 2016

Equilibrium Environmental Inc.

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• Exova
• Petroleum Technology Alliance of Canada (PTAC)
• PTAC Boron Working Group
• Environment Canada
• Alberta Environment and Parks

Acknowledgements

Presentation Overview

• Background and Existing Guidelines
• Boron Adsorption and Kd 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

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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 →

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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

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Image from: ‘http://californiaagriculture.ucanr.org/landingpage.cfm?Article=ca.v063 n01p 41&fulltext=yes’

California – ‘Red Rock Ranch’ showing residual salts including selenium and boron

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 Kd values

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Boron Adsorption and Kd Values

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Boron Adsorption in Soil – Kd Aspects

• Kd (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, Kd which is defined as:

Kd = adsorbed boron (mg/kg) dissolved boron (mg/L)

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Example dataset Kd can be estimated from slope: HWS B (mg/kg) = Kd + Sat% sat paste B (mg/L) 100

Boron Adsorption in Soil – Kd Aspect

• Used this technique for over 2,300 data points from over 40

sites across Alberta spanning a range of soil textures

• Kd correlated to texture via saturation percentage

(sat % a proxy for texture, see Equilibrium 2014 PTAC presentation)

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1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 HWS ¡B ¡(mg/kg) sat ¡paste ¡B ¡(mg/L) <43% 43-­‑100% >100%

ZOOMED IN

Guideline Derivation for Soil Dependent Biota

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Plant toxicity testing

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• Recent toxicity studies carried out by Exova (Edmonton lab) on

agricultural and boreal plant species

• Example responses and 25% effect levels shown below

25 50 75 100 125 150 0.0 0.1 1.0 10.0 100.0 1000.0 % of control Saturated paste boron (mg/L) SL-organic RL-organic SB-organic RB-organic SL-artificial RL-artificial SB-artificial RB-artificial SL-mineral RL-mineral SB-mineral RB-mineral

White spruce

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Northern Wheatgrass Alfalfa Carrot Durum Wheat Darlene.Lintott@exova.com Jack Pine

Plant Toxicity Testing

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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

Soil Dependent Biota – Plants (literature)

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• 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
• IC25’s estimated for cases where clear dose-response observed
• 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 (IC25’s)

Examples

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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

Soil Dependent Biota – Soil Invertebrates

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• Recent Exova research in combination with toxicity data from

published literature and method development studies was combined to derive IC25’s across species and soil types

– Substantial work done by Environment Canada, Method Development Unit

• Reproductive endpoints used to derive IC25’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

Guideline to Protect Soil Dependent Biota

• Direct eco-contact guideline derived based on the

ranked IC25s 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 IC25s 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 (25th percentile) 3.3 mg/L sat paste B Commercial/Industrial (50th 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

• Consistent with salinity, which measures conductivity in saturated paste

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Soil Dependent Biota-Combined Ranked IC25s

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Species Sensitivity Distribution (SSD)

Livestock and Wildlife Toxicity

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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

IC25s

• 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

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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

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• 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

Livestock and Wildlife Exposure

• Shown graphically, all exposures ratios are <1

(i.e., below thresholds) –implies minimal risk from food

22 No/minimal effect doses (from literature tox studies) Estimated daily exposures from consuming plants grown in soil at 3.3 mg/L sat paste B

• Exposure to B from soil ingestion negligible compared to food
• Exposure to B in drinking water assumed to be 25% of threshold
• All exposure ratios below 0.75 (75%), indicating minimal risk to

livestock and wildlife from food, soil, and water

Groundwater Pathways and Guidelines

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Guidelines to Protect Groundwater Pathways

• Groundwater guidelines can be converted to generate soil

guidelines in mg/L sat paste to protect groundwater pathways:

– Irrigation water

• Human drinking water

– Aquatic life

• Livestock drinking water
• Uses Alberta Environment Tier 1 methodology (similar to CCME):

Soil guideline = GW guideline x DF1 x DF2 x DF3 X DF4

“Dilution Factors” (DF1, DF2, DF3, DF4):

24 *Assumes impacts in the vadose zone, 10 m x 10 m source dimensions, 10 m to FAL

DF2 DF1 DF3 DF4

Guidelines to Protect Groundwater Pathways

DF1: Partitioning:

• The DF1 equation below has been modified from the Tier 1 protocol to

express the ratio between saturated paste boron and soil solution boron at a given soil moisture content. It is based on estimated Kd values

• A typical DF1 for fine soil is 0.823 and for coarse soil is 0.767

DF2: Vertical transport through vadose zone:

• =1, assumes impacts immediately above water table

DF3: Dilution into fine or coarse groundwater:

• ~3-5, depends on pathway and soil texture. Higher for DUA pathway

DF4: Lateral biodegradation/dispersion to aquatic life:

• ~1, very little dispersion during 10 m travel. No degradation

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Guidelines to Protect Groundwater Pathways

• Alberta Tier 1 groundwater and surface water boron

guidelines converted to soil guideline for each receptor:

• Since similar results for both textures, average of the fine and

coarse guidelines used as overall guideline for irrigation, aquatic life and livestock pathways * Tier 2 adjustments may be required if source length is >10 m. Adjustments have substantial effects on DUA pathway

26 3.4 mg/L 5.0 mg/L 17 mg/L

65 mg/L 120 mg/L

Other Pathways and Guidelines

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• Human direct soil contact guidelines estimate exposure from

ingested, inhaled, and dermally absorbed boron from soil

– relatively low-risk pathways under typical circumstances

Agricultural, Residential / Parkland = 7,500 mg/L sat paste B Commercial = 11,000 mg/L sat paste B Industrial = 230,000 mg/L sat paste B

• Soil guidelines also derived for off-site migration from industrial &

commercial land to more sensitive land uses:

– also relatively low-risk pathways under typical circumstances

• Risk to healthy soil nutrient cycling pathways also assessed via a

literature review of bacterial and enzymatic soil processes

– data limited, but pathway less sensitive than soil dependent biota

• Boron toxicity to humans via occupational exposure or

accidental poisoning described in literature

– data generally sparse/anecdotal

• Detailed toxicity studies commonly performed on proxy

laboratory species such as rats, mice, and rabbits

Summary of Updated Alberta Tier 1 Boron Guidelines

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• Constrained by ecological direct soil contact (plants and

invertebrates) for most land uses including agricultural

• Constrained by aquatic life for commercial/industrial land
• Groundwater pathways may require Tier 2 adjustments,

could alter guidelines for individual sites

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Thank You Questions?

• Exova
• Petroleum Technology Alliance of Canada (PTAC)
• PTAC Boron Working Group
• Environment Canada
• Alberta Environment and Parks

* Full references provided in Alberta Environment Tier 1 technical boron document and supporting appendices

Acknowledgements