Toxicology Update
Tiffany Bredfeldt, Ph.D.
Toxicology Division
Texas Commission on Environmental Quality
Advanced Air Permitting Seminar 2015
Updates
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New Odor White Paper
Updated Odor Values
Reminder to Use New ESL Forms
Database in Progress
Why Do We Regulate Odors?
• Odor - leading cause of citizen complaints
• Required by the Texas Clean Air Act
• What is the role of the odor-based ESL?
– Prevent odor nuisance conditions
– Not necessarily odor detection
New Odor White Paper
• Approach to odor ESL derivation has
changed
• New approach uses a weight of
evidence evaluation
• Visit the Toxicology website for more
information
Odor White Paper: Why Change?
• Odor data is highly variable
• The reason for the variance is unclear
• The purpose of an odor-based ESL is
to prevent nuisance
• The goal is to produce a list of odor
ESLs consistent in the manner in
which they are derived
Odor: Previous Approaches
• Collect odor thresholds:
– Odor detection threshold - concentration at
which a certain percent of a panel of humans
detects odor
– Odor recognition threshold - concentration at
which a chemical is recognized specifically
– The 50% odor detection threshold is typically
used
Odor: Previous Approaches
• For chemicals with reported thresholds, the
50% odor detection threshold was used
• If more than one OD50 was available, a
geometric average was taken
• If data was considered of lower quality, the
lowest OD50 was taken
• For chemicals without odor detection
thresholds, generic odor values were derived
based on structure-activity relationships or
chemical class
Previous Approaches: Pitfalls
• Odor threshold data are highly variable
• Newer methodologies may be very
sensitive and may result in bias
• If older values have not resulted in an
odor complaint, should we change the
value to newer data?
Odor: Updated Approaches
• Process is similar
• Steps:
– Identify odor character
– Is the chemical potentially malodorous?
– Search for available odor threshold data
• Agency records may guide the decisions
regarding the odor ESL used
• Not all chemicals will have odor ESLs
• The focus is upon chemicals that
could cause nuisance
Not all chemicals smell bad
Isoamyl acetate
Limonene
Cis-rose oxide
Beta-damascenone
Beta-ionone
Ocimenol
Cinnamyl alcohol
Ethyl-2-methoxybenzoate
Methyl salicylate
Some chemicals smell bad
Trimethylamine
Ammonia
Hydrogen Sulfide
Methane
1,5-Pentanediamine
1,4-Butanediamine
2-Butene-1-thiol
3-Methyl-1-butanethiol
Odor: Updated Approaches
• If there is evidence that a chemical may
cause odor nuisance but only at high
concentrations, higher thresholds may be
used
• Examples:
– Acetaldehyde
– Propionaldehyde
• Odor recognition threshold may be used
Example: Propionaldehyde
• Previous value (OD50): 22 µg/m3
• Odor is described as fruity at lower
concentrations
• Upon evaluation of available monitoring
data, this value has been detected at
sites where the odor was described as
sweet by field investigators
• New value (OR50): 95 µg/m3
Odor: Updated Approaches
• When selecting odor-based values:
– Consider odor character
– Determine odor if odor character is
ubiquitous or dependent on concentration
– Identify available odor thresholds
– Research past values used (if any) and
whether any odor complaints are
associated with this chemical
– Select odor threshold
Odor: Other Changes
• No generic odor values will be used anymore
(e.g., amines or carboxylic acids odor value)
• Instead, when odor values are not available,
ESLs will be surrogated to chemicals with
similar structure
• Values for chemicals where odor is described
as mild or pleasant will not be derived
• In those cases, health values will be used
• All odor ESLs were reviewed at the same time
• Consistent application of new guidance
Odor Summary
• Some approaches to how we derive odorbased ESLs have changed
• We will still derive odor ESLs as needed for
chemicals anticipated to be malodorous
• Detection or recognition thresholds may be
used as the basis
• New odor values may be seen in the updated
database
• And on our website
Additional Updates
• ESL Documentation
• ESL Database Project
Internet
ESL Documentation
• New form to fill out for ESL requests
• The paperwork processed during ESL
derivation has changed within the
Toxicology Division
• That means that ESL derivations may take
a bit longer due to the way records are
generated and placed into a format that
will be used for the database
• Expect a longer turnover time
ESL Documentation
• Make sure that you fill out the ESL request
form
• When consultants or companies ask for an ESL
for a specific chemical:
– Check current ESL list
– Fill out ESL request form
– Get additional information (i.e., MSDS, physical
chemical properties, etc.)
ESL Documentation
• Documentation may have slowed turn
around time
• We are releasing a new ESL list this fall
• Please remember to check our website
for ESLs
• New list will be publicized via the
Toxicology Announcements (e-mail)
Database
• The ESL database is still in the process of being
generated
• Some issues with getting it coded
• When complete, it should run through the public
database TAMIS
• In PROGRESS!
• Keep up with the Toxicology Division Announcements
online
Thank you for your attention
Tiffany Bredfeldt
tiffany.bredfeldt@tceq.texas.gov
512-239-1799