PBT Assessment of Hydraulic 

Fracturing Fluids from Coal Seam 

Gas Fields in Australia
• Joint venture partners expanding coal seam gas 

(CSG) fields in the Bowen Basins of Queensland

• A hydraulic fracturing quantitative risk assessment 

(QRA) is required as part of the Environmental 

Impact Statement (EIS) approval process

• The QRA evaluates the chemicals used in the 

stimulation (hydraulic fracturing) event to determine 

management measures to prevent potential risks to 

human health and the environment

• The science and fluids used in hydraulic fracturing 

are constantly evolving

• Based on geologic and hydraulic conditions in the coal 

seam formation, a broad mixture and variety of constituents 

are used

Introduction
Introduction
Introduction
Overall QRA Approach
• Evaluation and ranking of the relative hazards of 

hydraulic fracturing chemicals to identify the 

constituents that warrant detailed evaluation in QRA

• Lack of regulatory risk-based screening criteria for 

hydraulic fracturing chemicals

• An assessment of persistence, bioaccumulation, and 

toxicity (PBT) is a tool for evaluating the constituents 

that are potentially a concern to human health or the 

environment based on:

• Degrade or dissociate in the environment

• Bioaccumulate in terrestrial or aquatic species

• Exert toxic effect on human health or ecological receptors

• PBT information compiled in toxicological and 

environmental profile

Hazard Assessment
• Assessment of hazard and not potential risk

• QRA compares exposure levels of a hydraulic fracturing 

chemical by receptor to a maximum acceptable level without 

significant adverse effect

• PBT assessment does not consider exposure 

concentrations for most of the hydraulic fracturing 

chemicals

• Defines which hydraulic fracturing fluids may potentially 

present a risk

• If a threshold concentration is present based on the toxicity 

demonstrated in the PBT assessment

• The persistence and bioaccumulation that facilitates their 

potential for exposure by human and ecological receptors.

PBT Assessment
• Conducted using PBT Assessment guidance from 

Australia or the European Union’s Registration, 

Evaluation, Authorisation and Restriction of 

Chemicals (REACH) program

• One of the challenges in compiling the necessary 

PBT data is the proprietary nature of the constituents 

in the hydraulic fracturing fluids

• There may be limited robust experimental data available to 

assess PBT

• For constituents where the relevant data may not be 

available, appropriate modeling software may be 

used to obtain the data (i.e. US EPA EPISUITETM -

Estimation Programs Interface SuiteTM). 

PBT Assessment
• Chemical Risk Information Platform (CHRIP) [Japan] Information on Biodegradation and 

Bioconcentration of the Existing Chemical Substances Database 

http://www.safe.nite.go.jp/english/db.html 

• European Chemical Agency (ECHA) public database of Registration, Evaluation, Authorization 

and Restriction of Chemical Substances (REACH). registered substances (ECHA CHEM) 

http://apps.echa.europa.eu/registered/registered-sub.aspx 

• U.S. Environmental Protection Agency (USEPA) High Production Volume Information System 

(HPVIS) http://www.epa.gov/chemrtk/hpvis/index.html

• New Zealand Environmental Protection Authority - New Zealand Hazardous Substances and 

New Organisms (HSNO) Chemical Classification Information Database (CCID) 

http://www.epa.govt.nz/search-databases/Pages/HSNO-CCID.aspx

• World Health Organization (WHO) International Programme on Chemical Safety (IPCS) 

Chemical Safety Information from Intergovernmental Organizations (INCHEM) 

http://www.inchem.org/

• Australian National Industrial Chemicals Notification and Assessment Scheme (NICNAS) 

Priority Existing Chemical (PEC) Assessment Reports 

http://www.nicnas.gov.au/Publications/CAR/PEC.asp

• OECD Screening Information Dataset (SIDS) Database OECD Existing Chemicals Screening 

Information Data Sets (SIDS) Database (in IUCLID software) 

http://oecdsids.jrc.ec.europa.eu:80/i5browser/Welcome.do

• OECD Initial Assessment Reports for HPV Chemicals including Screening Information Data 

Sets (SIDS) as maintained by United Nations Environment Programme (UNEP) Chemicals 

http://www.chem.unep.ch/irptc/sids/OECDSIDS/sidspub.html

Sources of PBT Data
US EPA EPISUITETM 
US EPA EPISUITETM 
US EPA EPISUITETM 
• The results of BIOWIN v4.10 for THPS are as follows: 

biodegrade fast (Biowin2); ultimate biodegradation 

timeframe is days-weeks (Biowin3); and biodegrades 

fast (Biowin 6)

• THPS does not meet the screening criteria for persistence. 

• The estimated log Kow for THPS using EPISUITE is -

20.39. Hydrolysis is also indicated as a significant 

abiotic degradation process

• THPS does not meet the screening criteria for bioaccumulation. 

• The NOEC from a 72-hr green algae study was 

reported to be 0.063 mg/L, which is <0.01 mg/L

• THPS meets the criteria for toxicity. 

• The overall conclusion is that THPS is not a PBT 

substance

PBT Profile: Tetrakis(hydroxymethyl) phosphonium 

sulfate (THPS)
Australia PBT Criteria

Criterion PBT criteria

Persistence For PBT purposes a chemical is considered persistent in a particular media if its 

half-life in the media exceeds the following:

Half life (T1/2) >2 months in water

Half life (T1/2) >6 months in soil

Half life (T1/2) >6 months in sediment

Half life (T1/2) >2 days in air

Bioaccumulative For PBT purposes a chemical is considered to be bioaccumulative if it has a 

BCF/BAF of >2000, or in its absence of any BCF/BAF measurement a log Kow

>4.2.

Toxic For PBT purposes, in respect of aquatic toxicity, a chemical may be considered 

toxic under the following circumstances (corresponding to criteria for GHS chronic 

category 1:

Non-rapidly degradable 

substances for which 

there are adequate 

chronic toxicity data 

available

Chronic NOEC or ECx

(for fish)

<0.1 mg/L and/or

Chronic NOEC or ECx

(for crustacea)

<0.1 mg/L and/or

Chronic NOEC or ECx

(for algae or other 

aquatic plants)

<0.1 mg/L 

Rapidly degradable 

substances for which 

adequate chronic toxicity 

data are available

Chronic NOEC or ECx

(for fish)

<0.01 mg/L and/or

Chronic NOEC or ECx

(for crustacea)

<0.01 mg/L and/or

Chronic NOEC or ECx

(for algae or other 

aquatic plants)

<0.01 mg/L 

Substances for which 

adequate chronic toxicity 

data are not available 

(providing criteria for P 

and B are met)

96 h LC50 (for fish) <1 mg/L and/or

48 h EC50 (for crustacea) <1 mg/L and/or

72 or 96 ErC50 (for alage 

or other aquatic plants)

<1 mg/L 

And the substance is not rapidly degradable and/or 

the experimentally determined BCF is >500 (or, if 

absent, the log Kow is >4.2

Toxicity to other 

(terrestrial) organisms

Should be considered on a case by cases basis, 

compared with the highly toxic classifications DotE

has developed for ag/vet chemicals

Long term toxicity or 

evidence such as 

endocrine disruption 

effects

Should be considered on a case-by-case basis.
REACH PBT Criteria

Type of Data Criterion Screening Assignment

Persistence

Ready biodegradability test Readily biodegradable Not P and not vP

Enhanced ready biodegradability 

test

Readily biodegradable Not P and not vP

Specified tests on inherent 

biodegradability

Zahn-Wellens (OECD 302B) >70% mineralization (DOC 

removal) within 7 d; log phase no 

longer than 3 d; removal before 

degradation occurs below 15%; no 

pre-adapted inoculum

Not P

MITI II test (OECD 302C) >70% mineralization (O2 uptake) 

within 14 d; log phase no longer 

than 3 d; no pre-adapted inoculum

Not P

Biowin 2 (non-linear model 

prediction) and Biowin 3 (ultimate 

biodegradation time)

or

Does not biodegrade fast 

(probability) and ultimate 

biodegradation timeframe 

prediction: >months (value <2.2) 

or

P

Biowin 6 (MITI non-linear model 

prediction) and Biowin 3 (Ultimate 

biodegradation time)

Does not biodegrade fast 

(probability <0.5) and ultimate 

biodegradation timeframe 

prediction: >months (value <2.2)

P

Bioaccumulation

Convincing evidence that a 

substance can biomagnify in the 

food chain (e.g., field data).

e.g., BMF >1 B or vB, definitive assignment 

possible

Octanol-water partition coefficient 

(experimentally derived or 

estimated by valid QSAR)

Log Kow < 4.5 Not B and not vB

Toxicity

Short-term toxicity aquatic toxicity 

(algae, daphnia, fish)

EC50 or LC50 <0.01 mg/L T, criterion considered to be 

definitely fulfilled

Short-term toxicity aquatic toxicity 

(algae, daphnia, fish)

EC50 or LC50 <0.1 mg/L T

Avian toxicity (subchronic or 

chronic toxicity or toxic for 

reproduction)

NOEC <30 mg/kilogram(kg) food T
REACH PBT Criteria
• A PBT Assessment was used to evaluate the potential 

for human health and environmental (e.g., ecological) 

risks by comparing a “green” fluid system to a previous 

water and guar based system that was assessed using 

the QRA process

• The results of the QRA indicated acceptable risks with 

implementation of operational and H&S management 

procedures, and spill containment procedures

• The “green” fluid system was developed as a more 

environmentally fluid system than their original 

formulation, the composition is similar with substitutions 

for less hazardous chemicals

• For chemicals assessed in the “green” fluid system, 

none were considered to be inherently hazardous, and 

potential risks were no greater than original fluid system

Comparison of Fluid Systems
• Marcellus Shale Coalition develops guidance for the 

hydraulic fracturing operations within the Marcellus Shale

• A key consideration is the evaluation and assessment of 

current and proposed additives for the drilling and 

completion process

• One tool to use in this evaluation process could include 

the PBT Assessment

• Relatively quick and cost-effective method to evaluate proposed 

substitutions or new fluid systems to be used

• Part of an educational source of tools and references to take into 

consideration to evaluate the selection of fluid additives and 

subsequent blends / formulations

Marcellus Shale Gas
Questions