Schmidt, L.J., Gaikowski, M.P., Gingerich, W.H., Stehly, G.R. and W. J. Larson. 2002. 
Use of chloramine-T in intensive fresh-water aquaculture: An evaluation of potential 
environmental fate and effects. Submitted to U.S. Food and Drug Administration Center 
for Veterinary Medicine on October 31, 2002.
Executive Summary
Introduction
This environmental report provides an examination of the possible environmental effects 
of chloramine-T discharge into fresh-water ecosystems after use as a therapeutant in 
aquaculture. The report presents (1) a summary of the scientific literature relevant to 
present uses, potential impacts, and environmental fate and effects of chloramine-T; (2) a 
risk characterization for intensive aquaculture use on the basis of combined data from the 
publicly available scientific literature and results of a recent U.S. Geological Survey 
(USGS) survey conducted by the Upper Midwest Environmental Sciences Center 
(UMESC) detailing the projected use and discharge patterns of chloramine-T at public 
and private United States aquaculture facilities; and (3) tables, figures, and appendixes 
that include fate models, hatchery schematics, projected hatchery use data, and hatchery 
discharge estimates given as Environmental Introduction Concentrations (EICs), a 
regulatory term essentially meaning the concentration discharged into the environment. 
Approval is presently being sought for the use of chloramine-T as a waterborne 
therapeutant in aquaculture to control mortality associated with bacterial gill disease in 
cultured fresh-water fish.
Present Uses
Chloramine-T has been used in water solution throughout most of the 20th century in 
Europe as an antiseptic and is still used for that purpose today. Perhaps its most common 
use is as a disinfectant or sanitizing agent in the food, beverage, poultry, and dairy 
products industries. Chloramine-T recently has been used in intensive aquaculture to 
control mortality associated with bacterial gill disease in cultured fresh-water fish under 
an Investigational New Animal Drug (INAD) permit from the U.S. Food and Drug 
Administration. Chloramine-T therapy also shows promise to control mortalities 
associated with other external flavobacterial infections. Outside the United States, 
chloramine-T is used in Canada, Scotland, Ireland, Norway, and Chile to treat external 
bacterial infections on cultured fish.
Aquaculture Use Model
For the purposes of this assessment, we define an environmental model in which 
chloramine-T may be discharged after aquaculture use. A discussion of site 
characteristics, potential impacts, environmental fate and effects, and a risk 
characterization are presented for the model. Although the potential for chloramine-T 
discharge into brackish-water ecosystems exists, we did not identify any hatcheries that 
discharged into brackish-water ecosystems in a survey of 100 hatcheries, nor were there 
any toxicity data available for chloramine-T in brackish water. Therefore, this risk 
characterization discusses the potential risk associated with discharge into fresh-water 
lentic or lotic systems.
Degradation
Chloramine-T is naturally dechlorinated to para-toluenesulfonamide (p-TSA) and by 
chlorine exchange to a number of theoretically possible (usually mono-) chlorinated 
organic compounds, each at low concentrations. Stability of the degradation process is 
reached when a compound is formed that is not likely to give up its acquired chlorine. 
The number of such compounds may be theoretically large, and all will be at low 
(generally sub-g/L) concentrations. The time to degrade all chloramine-T in natural 
waters will vary from a few hours to more than a week, depending on the composition of 
the discharge and receiving waters.
Environmental Fate
The potential chloramine-T upper label limit on the basis of present efficacy, target 
animal safety, and human food safety studies is 20 mg/L (about 5 mg/L as Cl2). The 
primary mechanism for reducing chloramine-T concentrations in water after treatment 
and thus its toxicity before discharge to receiving water is dilution, except in jurisdictions 
that require mitigation. Degradation may also be important in some hatchery waters, 
especially those with holding ponds, but this mechanism cannot be reliably estimated by 
the aquaculture facility unless deliberate mitigation takes place. On the basis of estimates 
provided from a USGS survey of 100 United States private and public hatcheries, two 
potential discharge types are possible from the 60 hatcheries that indicated a potential for 
chloramine-T use. In the majority of the hatcheries, the USGS survey data predict 
relatively short-duration, intermittent pulsed exposures that last less than 12 h (49 of 60 
hatcheries); 93% of hatcheries were estimated to discharge for less than 29 h. For all 
hatcheries that reported chloramine-T use, the median typical EIC was estimated to be 
1.1 mg/L (mean = 2.2 mg/L, 95% confidence interval = 1.52.9 mg/L) whereas the 
median maximum EIC was estimated to be 1.7 (mean = 2.8 mg/L, 95% confidence 
interval = 2.033.65 mg/L). Hatcheries that discharged for longer than 12 h were 
estimated to have a mean typical EIC of 0.1 mg/L and a mean maximum EIC of 0.2 
mg/L. The estimated EICs presented within this report probably overestimated the 
concentrations actually achieved within the aquatic environment because our model only 
describes dilution within the hatchery and completely discounts the following parameters: 
(1) the reduction in chloramine-T concentration from chlorine demand within hatchery 
water, (2) dilution within the receiving water, and (3) additional chlorine demand within 
the receiving water.
Degradation in hatchery and receiving waters could be substantial in many instances, but 
it is likely to differ greatly by facility. Most, if not all, receiving water bodies have a 
dilution potential at least equal to, if not much greater, than that of the hatchery. After 
discharge, degradation by chemical mechanisms to stable chlorinated organics, p-TSA, 
and long-term degradation products (presently unknown) of p-TSA typically produces 
products at ultratrace concentrations, well below those that can be detected by analytical 
instrumentation for any of the chemical species involved. In most circumstances, the 
concentration of chloramine-T and all associated breakdown products in the receiving 
water would probably be reduced to concentrations below detection within a few hours 
after discharge from the hatchery is complete.
Environmental Effects
The environmental effects of chloramine-T depend heavily on whether it and its chlorine 
exchange products are mitigated before the hatchery effluent is released to public waters. 
On the basis of the predicted chloramine-T discharge concentrations and available 
toxicity data, there is the potential for chloramine-T and possibly some of its breakdown 
products to pose some risk to the environment or to aquatic life. The risk associated with 
chloramine-T discharge depends on the concentration released and on the duration of 
release. Fish are relatively tolerant to chloramine-T and concentrations up to 20 mg/L are 
generally considered safe for brief exposures (<1 h). Other vertebrates and mammals are 
much more tolerant than fish. The likelihood of exposure and effects on terrestrial life are 
believed to be negligible and are not addressed in this environmental report. No long-
term effects to microbial organisms are expected to result from chloramine-T use in 
aquaculture. Toxic effects to microorganisms in the environment are probably minimal, 
considering the relatively short exposure times to potentially toxic chloramine-T 
concentrations, because of rapid dilution and degradation of discharged chloramine-T and 
the ability of microorganism populations to rebound and/or repopulate from ubiquitous 
sources after exposure.
Risk Characterization
In this environmental assessment, we demonstrate that
1. Chlorine use as chloramine-T at aquaculture facilities is substantially less than that of 
the large users of water chlorinating chemicals (wastewater treatment, pulp mill, and 
electric power industries), and the number and frequency of discharges are far fewer (on 
the basis of a USGS survey, about 10 therapies for a total of about 40 discharges per year 
per aquaculture facility using the chemical). Thus, in contrast to the wastewater treatment 
industry, discharges at aquaculture facilities occur only on a sporadic basis.
2. Chloramine-T use at hatcheries will not produce aqueous free chlorine (HOCl + OCl-) 
or inorganic (ammonia) chloramines such that discharge concentrations will be above 
0.011 mg/L total free chlorine plus inorganic chloramines (both stated as Cl2), the 
concentration at which they become a concern to regulatory agencies.
3. Chloramine-T mostly degrades by monochlorinating the compounds that comprise 
chlorine demand. Thus, it produces negligible amounts of potentially mutagenic 
electrophilic organochlorines that are usually polychlorinated or polyhalogenated, such as 
the trihalomethanes.
4. The large number of theoretically possible organic chloramine and other chlorinated 
organic compounds that might be produced at low individual concentrations from 
chlorination of their precursors by chloramine-T, because of the presence of the many 
nitrogenous and other organic compounds in natural waters, are mostly less toxic than 
chloramine-T, and their overall toxicity is less than that of chloramine-T itself.
5. Nonhalogenated breakdown products of chloramine-T (primarily p-TSA, a relatively 
stable chemical) will not be a significant threat to organismal, environmental, or public 
health.
6. Discharged products of thiosulfate- or sulfite-mitigated chloramine-T will not be a 
significant threat to organismal, environmental, or public health.
7. Free chlorine and inorganic chloramines are more than 10 times as toxic as 
chloramine-T. They, not chloramine-T, are the compounds upon which the U.S. 
Environmental Protection Agency (EPA) has recommended effluent limits for total 
residual chlorine (TRC).
8. At ambient ranges, temperature and hardness do not play a significant role in risk 
associated with chloramine-T effluent. However, exposure in acidic waters (pH 6.5) 
increases chloramine-T toxicity with a 6- to 20-fold decrease in 96-h LC50 versus pH 
9.5. Our risk-assessment calculations account for the changes in mortality because of pH.
9. Direct contact of organisms with waterborne chloramine-T and its degradation 
products is the only exposure mechanism of concern for assessing environmental risk.
We used the standard indices referred to as Hazard Quotient and Risk Quotient as the 
primary basis for risk analysis. These quotient analyses are a ratio of estimated EICs 
(concentrations at the discharge pipe) to selected toxicological endpoints. The risk 
analyses do not take into account any degradation within the hatchery effluent, immediate 
dilution of chloramine-T after release to public waters, or any degradation of chloramine-
T that would occur both in the hatchery and in the aquatic ecosystem. We chose to 
estimate risk on the basis of EIC estimates, an uncommon practice, because chloramine-T 
is detected by most EPA tests as TRC and, therefore, may be evaluated by regulatory 
agencies on the basis of discharge concentrations. However, we believe the data within 
this report suggest that chloramine-T toxicity is much less than that expressed by TRC. If 
this is so, the risk associated with chloramine-T discharge from intensive aquaculture 
facilities could have been more appropriately modeled using the commonly employed 
estimated environmental concentration (EEC), an estimate of the concentration within the 
receiving water body at some time after discharge. Had we used EEC estimates in our 
quotient analysis, our quotient estimates would have been substantially less than those 
developed on the basis of our EIC estimates.
In our risk analyses, we sought to identify potential acute risks that might pose a threat to 
certain aquatic populations at both typical and maximum estimated EICs. Our risk 
calculations associated with acute effects, however, were based on toxicological baseline 
values from exposures that are generally 2 to 20 times the discharge duration expected 
from most hatcheries. Chronic toxicity data for chloramine-T were limited to one 
invertebrate species and pulsed-exposure data for walleye Stizostedion vitreum and 
channel catfish Ictalurus punctatus; our risk analysis did not identify the potential for 
long-term risk for fish or invertebrates on the basis of the available data from chloramine-
T use at hatcheries. The acute and chronic toxicity data for p-TSA also support our 
conclusion that chloramine-T use poses little, if any, long-term risk in the aquatic 
ecosystem. Any hatchery that theoretically has a long-duration discharge of chloramine-T 
would most likely be discharging that chloramine-T as p-TSA, a compound that is much 
less acutely toxic. In actual situations, chloramine-T discharge at concentrations similar 
to the typical or maximum EIC values reported are not likely to result in acute or chronic 
effects of concern on any aquatic species population in all but the smallest receiving 
streams.
Nonetheless, we propose the establishment of a 1 mg/L chloramine-T maximum effluent 
discharge concentration from hatcheries in order to make the worst-case event be at a 
known concentration that has well-established effects on the basis of the data presented in 
this environmental report. A discharge limit of 1 mg/L does not eliminate all potential 
toxic effects to aquatic life, but does minimize risk of mortality or long-term population 
effects. This maximum discharge concentration would appear on the label, as shown in 
Section 3.0.
Conclusion
Under use practices at most hatcheries, we believe that the use of chloramine-T as a 
waterborne therapeutant in intensive aquaculture operations for the control of mortalities 
associated with external bacterial infections of cultured fish and subsequent discharge at a 
proposed discharge limit of 1 mg/L constitutes no actual threat to the environment, the 
populations of organisms residing there, or public health and safety.