From:
Kolodziej, Christopher <ckolodziej**At_Symbol_Here**EHS.UCLA.EDU>
Subject:
Re: [DCHAS-L] Phenolphthalein or Replacement?
Date:
Nov 13, 2025 17:16 UTC
Reply-To:
ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU>
Message-ID:
<DM8PR04MB7766AE5649DDDA9C7DC7D9CEF7CDA**At_Symbol_Here**DM8PR04MB7766.namprd04.prod.outlook.com>
In-Reply-To:
<42848d6e-f1c5-4f89-a5c7-abe366b40999**At_Symbol_Here**retired.appstate.edu>
Two questions regarding the interpretation David forwarded:
-
As far as I can tell, D022 is the waste code for chloroform, not phenolphthalein. What am I missing?
-
The D list provides threshold concentrations below which a mixture is not considered toxic. Phenolphthalein does not appear to be a listed waste that would trigger a hazardous
classification at any concentration (based on searching
https://www.ecfr.gov/current/title-40/chapter-I/subchapter-I/part-261/subpart-D and
https://www.ecfr.gov/current/title-40/chapter-I/subchapter-I/part-261/appendix-Appendix%20VIII%20to%20Part%20261). Is there another list that I’ve overlooked?
If I am on the right track, then this would not be a RCRA hazardous waste. That still leaves
open Jeff’s point that drain disposal could be in violation of a local ordinance or contract obligation. For example, our industrial wastewater permit prohibits alcohols from being disposed to the sewer. Interpreted broadly, that would include phenolphthalein.
At that point it becomes a practical question of institutional risk tolerance and prioritization.
Chris
________________________________
Christopher M. Kolodziej, Ph.D.
Chemical Hygiene Officer
UCLA Environment, Health & Safety
| Chemical Safety
Phone: (310) 794-5013
Book a virtual appointment
My working hours may not be your working hours. Please do not feel obligated to reply outside of your normal work schedule.
From: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU>
On Behalf Of Samuella Sigmann
Sent: Thursday, November 13, 2025 7:02 AM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: Re: [DCHAS-L] Phenolphthalein or Replacement?
Like Rob, I am wondering about characterizing this as toxic. Seems to me that it could be considered de minimus. I would check with my local water treatment plant and have them weigh in.
That said, I am no haz waste expert.
Sammye
On 11/12/2025 6:50 PM, David EldrEdge wrote:
I see where you are coming from. I am virtually on the same page, and I brought your argument up with our EHS representative.
"Phenolphthalein should not be poured down the drain. It is classified by the EPA as a toxic hazardous waste (D022) under 40 CFR §261.24 – Toxicity Characteristic due to its potential carcinogenic properties.
Any solutions, residues, or contaminated materials containing phenolphthalein must be collected and disposed of through the hazardous waste program, not through the sanitary sewer.
Please label any waste containers as “Phenolphthalein Waste – Toxic (D022)” and store them in your designated hazardous waste accumulation area until Environmental Health & Safety can arrange for proper disposal. Hope this helps"
I have not had any firm responses about other indicators such as bromthymol blue. I am led to believe then, this is a safe alternative to phph and we can therefore send our neutralized NaOH and HCl, down the drain with bromthymol blue.
435.767.7714 Google Voice & Text
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I am a complete neophyte with respect to waste regulations. Can someone please explain why this conversation is even happening? I can’t see any statistically possible way pouring this down the drain poses a risk to anyone or anything. To
wit:
Phenolphthalein is normally used as a 1% by mass solution at most - usually 0.1% if titrating a dilute or weak acid. And one uses one or two drops per titration; maybe three if 0.1%.
So even if I had a full lab class of 24 students and each did 3 titrations that afternoon, that’s maybe 150 or even 200 drops - less than half an ounce.
Half an ounce is about 15 mL. At 1% by mass that’s 0.15 g of phenolphthalein, 150 mg. Figure with glassware washing and whatnot, each student is going to put at least 4 gallons down the sink so call it
100 gallons total, or 400 liters in round numbers.
Phenolphthalein has a molar mass of 318 g/mol, so we’re talking 0.0004717 moles. In 400 liters of water. So it’s 0.00000118 molar. Which is 0.375 ppm in the waste stream. And that’s before being diluted by the rest of the building and
campus which will take that down another couple orders of magnitude.
1. I doubt any wastewater authority would be looking for, let alone be able to detect, what will ppb levels of the stuff where it hits the monitoring point.
2. Sure, phenolphthalein is a suspected human carcinogen but according to the 15th NTP Rerpot on Carcinogens “The data available from epidemiological studies are inadequate to evaluate the relationship between
human cancer and exposure specifically to phenolphthalein.” And that’s from looking at people that
ingested 5-10 mg (or more) orally over long periods of time (to get a 5 mg dose from our 0.375 ppm waste stream would require drinking 13 liters of it). Even in the rodent models, it took fantastically high dosages to produce effects (hundreds or thousands
of ppm daily).
3. So this clearly comes down to Regulations somewhere.
So, what specific Regulation is being applied here, is it bound by hazard (regardless of risk) vs the risk (which is based on the actual amount) or some absolute ppm level, and is this something local wastewater authorities can mandate
on their own?
When I checked a couple of SDSs for phenolphthalein solution they indicated they were mixed with ethanol and had a flashpoint below 60c, which makes the stock solution ignitable and a characteristic hazardous waste. Presumably you are
diluting it as part of a reaction. If the alcohol is diluted to less than 24% it is no longer a characteristic hazardous waste (by definition) but may still be ignitable and prohibited by the sewer authority.
I found two different SDSs for bromothymol blue solution, one of which used IPA and, again, a flashpoint less than 60C.
But, even if you use an aqueous based dye you might still be not allowed to sewer it; some sewer authorities have prohibitions from dyes being sewered.
Hence, it should be collected for waste disposal, the question is does it meet the RCRA definition of a hazardous waste (EPA code D001) or is it collected and disposed of as a nonRCRA (Liquid Industrial Byproduct in MI) waste?
Our School's EHS responded to a question that was brought up about phenolphthalein:
"I verified this with the wastewater district, and they confirmed that it [phenolphthalein] cannot be disposed of down the drain. I want to be cautious here if we
start discharging materials improperly, it could trigger a wastewater audit and potentially open Pandora’s box for the college."
What do you all do? Are you still using phenolphthalein or have you replaced phenolphthalein with something like bromthymol blue or something similar? Do you get the same results or better?
Are you still using phenolphthalein, if so how do you deal with the waste? If collecting the waste, is it worth the cost of disposal?
435.767.7714 Google Voice & Text
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Jeff Lewin
Environmental Health and Safety
Office of the General Counsel
Michigan Technological University
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--- For more information about the DCHAS-L e-mail list, contact the Divisional membership chair at
membership**At_Symbol_Here**dchas.org
--- For more information about the DCHAS-L e-mail list, contact the Divisional membership chair at
membership**At_Symbol_Here**dchas.org
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