Copper sulfate

Why roots end up in sewer lines

Roots get in through small cracks and poorly sealed joints in sewer lines. Left alone, they keep growing in number and size, causing breaks, slow flow and finally a complete stoppage. The label describes copper sulfate as a known way to control roots in residential and commercial sewers.^[1]

The crystals have to reach the roots, so the label stresses treating while some water still flows. Roots take up the copper sulfate and usually die within 3 to 4 weeks; when they grow back, the line needs another treatment.^[1]

Treating algae in a pond

Water hardness, water temperature, the kind and amount of growth and the water flow all change how much it takes. Algae are hard to control when the water is below 60°F or its alkalinity is above 50 ppm, and flowing water needs more than still water. Starting soon after growth begins takes less product than waiting until algae are heavy.^[1]

If possible, stop the flow before treating and hold the water for about three days, or until the algae begin to die. To dissolve the crystals, use a plastic, glass, or painted, enameled or copper-lined metal container, and treat on a sunny day, when mats of filamentous algae are most likely floating where they can be sprayed.^[1]

Dying algae use up oxygen as they decay, and that can suffocate fish. The label says to treat no more than half of the water area at a time, wait at least 14 days between treatments, and start along the shore and work outward in bands so fish can move into untreated water.^[1]

Most algae respond to 1 to 2 ppm of copper sulfate crystals, and EPA's maximum is 4 ppm (1 ppm of metallic copper). If the water will be a source of drinking water, the copper left in it must not exceed 1 ppm of metallic copper (4 ppm of crystals). The label's worked example: one acre-foot of water weighs 2,720,000 pounds, so a 2 ppm treatment takes 5.44 pounds of crystals.^[1]

Treating a dense bloom of cyanobacteria can release toxins from inside the cells, some of which harm the liver and nervous system in mammals. The label says to manage these blooms so you avoid treating when toxin-producing species are present at high density.^[1]

Copper doesn't break down

Unlike most organic pesticides, copper is an element. The label warns that it won't break down in the environment and builds up in sediment with repeated applications, and that, although copper is a micronutrient, its pesticide application rate is more than is needed as a nutrient.^[1]

NPIC says copper in soil collects mainly at the surface, where it binds tightly and persists. Plants regulate copper because it is an essential mineral, but too much inhibits photosynthesis.^[3]

EPA hasn't published a cancer rating for copper sulfate. NPIC says that's because of a lack of evidence linking copper or copper salts to cancer in animals that can normally regulate copper in their bodies.^[3]

Where it is used

Copper sulfate has been registered in U.S. pesticide products since 1956. NPIC counts several dozen active products, sold as liquids, dusts or crystals, and some are approved for use in organic agriculture.^[3]

The residential use labeling on Copper Sulfate Crystals is for subregistrants' packages of 20 ounces to 15 pounds, which state that they're intended for residential or homeowner use only. It covers roots in household sewer lines, septic tanks and leach lines, and algae in ponds, lakes and other impounded water.^[1]

The main label, for 25- to 60-pound bags, adds commercial, institutional and municipal sewers, sewer pumps and force mains, storm drains, algae and aquatic weeds in irrigation ditches and reservoirs, and Bordeaux mixture sprays for crops such as almonds, peaches, cherries, blueberries, citrus and ornamental bulbs.^[1]

Roebic K-77 Root Killer (EPA Reg. No. 7792-1) is the same 99% copper sulfate pentahydrate in a 2-pound bottle, labeled only for killing roots in sewer and septic pipes, with the signal word DANGER.^[2]

In New York State waters it is a restricted use aquatic pesticide, so selling, possessing or using it there takes pesticide applicator certification or a special use permit.^[1]

Products and registrations

Label rates

How to apply it, step by step

Steps for Roebic K-77 Root Killer (99% copper sulfate pentahydrate, 25.1% metallic copper; 2-lb bottle), EPA Reg. No. 7792-1, taken from its label^[2]. Other products with this active ingredient have their own labels; follow yours.

1. Protective gear

• The signal word is DANGER. The label calls the crystals corrosive and says they cause irreversible eye damage, may be fatal if swallowed and are harmful if absorbed through skin.^[2]
• Wear safety glasses. Keep the crystals out of your eyes and off your clothing, and avoid skin contact.^[2]
• Wash thoroughly with soap and water after handling and before eating, drinking, chewing gum or using tobacco. Take off and wash contaminated clothing before wearing it again.^[2]

2. Before you spray

• Never put the crystals into a tub or sink drain.^[2]
• Depending on where it's sold, the package may carry state limits: Connecticut doesn't allow its use in sewage systems; it isn't for sale or use in the California counties of Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano and Sonoma; and it isn't for use in septic systems in Florida or Massachusetts.^[2]
• Don't apply it in a way that will contact adults, children or pets, either directly or through drift.^[2]
• It must not be used in any municipal or public storm sewer, or in any storm drain system covered by a stormwater (MS4) discharge permit.^[2]

3. Mixing

• Nothing is mixed: the crystals go in dry. One treatment is the whole 2-pound bottle, flushed down in portions of 0.67 pound (0.17 pound of metallic copper) at a time.^[2]

4. Applying

• Use it at night, before going to bed.^[2]
• Pour 0.67 pound of crystals into the toilet bowl and flush, then immediately repeat until all of the product has been flushed into the sewer pipe. Low-flow toilets may need extra flushes to clear the crystals from the bowl.^[2]
• With a septic system, you can instead add the contents directly to the drainfield through the distribution box. Add 2 to 3 gallons of water to carry the crystals to the roots in the pipes.^[2]

5. After you spray

• The label says it kills existing roots in pipes. Retreatments at 6- to 12-month intervals may be needed for new or unusually heavy root growth, with no more than two applications per calendar year.^[2]
• The yearly ceiling is 1 pound of metallic copper (4 pounds of product) per linear foot of pipe.^[2]
• The label says it works year round without harming surrounding trees, ground cover or the natural bacteria in septic tanks and cesspools.^[2]

First aid

• If in eyes: hold the eye open and rinse slowly and gently with water for 15 to 20 minutes. Remove contact lenses after the first 5 minutes, then keep rinsing. Call a poison control center or doctor for treatment advice.^[2]
• If swallowed: call a poison control center or doctor immediately. Have the person sip a glass of water if able to swallow. Don't induce vomiting unless the poison control center or doctor tells you to, and give nothing by mouth to an unconscious person.^[2]
• If on skin or clothing: take off contaminated clothing, rinse skin immediately with plenty of water for 15 to 20 minutes, and call a poison control center or doctor.^[2]
• Have the container or label with you when you call or go for treatment. For emergency assistance the label gives 1-800-424-9300. Its note to physicians says probable mucosal damage may rule out gastric lavage.^[2]

Storage, spills and disposal

• Store it in a dry place, away from food or feed and away from children. Don't contaminate water, food or feed by storage or disposal.^[2]
• Don't reuse or refill the container. Put an empty one in the trash or recycle it where available. For a partly filled container, call your local solid waste agency for disposal instructions. To get rid of leftover product, the label says never to put it down any indoor or outdoor drain.^[2]

From the safety data sheet

From the product's safety data sheet^[6]. Where it and the label differ, the label is the law.

• Roebic Laboratories' safety data sheet for K-77 Root Killer (EPA Reg. No. 7792-1; issued May 22, 2015) lists more than 99% copper (II) sulfate pentahydrate, blue odorless crystals. Its GHS signal word is Warning, while the pesticide label hazard text it reproduces is headed DANGER.^[6]
• Its GHS classes are acute oral toxicity Category 4 (harmful if swallowed), acute dermal toxicity Category 5, skin irritation Category 2, eye irritation Category 2 (causes serious eye irritation), and Category 1 for both acute and chronic aquatic toxicity (very toxic to aquatic life with long lasting effects).^[6]
• The toxicology section gives an oral LD50 of 352 mg/kg in rats and a dermal LD50 above 5,050 mg/kg in rabbits, rates the crystals an eye and skin irritant, and notes they aren't listed as a carcinogen by NTP, IARC or OSHA. Poisoning may affect the liver, kidneys and gastrointestinal tract, and people with chronic respiratory or skin disease may be at greater risk from exposure.^[6]
• For wildlife it lists 96-hour LC50 values of 0.65 ppm for bluegill and 0.056 ppm for trout, and a subacute dietary LC50 above 10,000 ppm for quail and duck.^[6]
• The crystals aren't flammable, but in a fire they can break down into sulfur oxides and copper fumes. They absorb moisture but stay stable when kept dry, can corrode aluminum, steel and iron, and should be kept away from magnesium, strong bases, phosphates, acetylene, hydrazine and zirconium.^[6]
• For a spill, keep people out of the area, avoid all skin contact, and vacuum the material up to avoid creating dust, then seal it in containers for disposal.^[6]

Need the amount for your sprayer? Use the mixing calculator, which works from the same label rates.

Safety and environmental hazards

People

The label's signal word is DANGER: it calls the crystals corrosive, causing irreversible eye damage, possibly fatal if swallowed and harmful if absorbed through skin. NPIC says copper sulfate can cause severe eye irritation, and that eating large amounts can cause nausea, vomiting and damage to body tissues, blood cells, the liver and kidneys, with shock and death in extreme exposures.^[1][3]

Pets

NPIC says copper sulfate affects animals much as it does people: signs of poisoning include loss of appetite, vomiting, dehydration, shock and death, and diarrhea and vomit may be green to blue. Dalmatians and Bedlington, West Highland white and Skye terriers are particularly sensitive to copper because of a genetic defect. The label says to keep adults, children and pets out of treated areas until sprays have dried or dusts have settled.^[3][4][1]

Bees and pollinators

NPIC reports that EPA considers copper practically nontoxic to bees. The label carries no bee warning.^[3][1]

Fish and water

The label says the product is toxic to fish and aquatic organisms, and that copper, being an element, doesn't break down and builds up in sediment with repeated applications. NPIC describes copper as highly to very highly toxic to fish and aquatic life, with trout, koi and juvenile fish particularly sensitive, and notes fish kills after algae treatments in ponds and lakes, with oxygen depletion and increased debris from suddenly dying algae and plants cited as the cause of most of those deaths.^[1][3]

Common questions

Can I pour copper sulfate root killer down the kitchen sink?

No. The label says not to put it through sink or tub drains because it will corrode metal drains. It goes into the toilet nearest the sewer line, about ½ pound per flush, or straight into the line through a cleanout.^[1]

Will it kill the tree whose roots are in my sewer line?

Normally not. The label says trees and shrubs near a treated line usually aren't affected, because only a small part of their roots touches the crystals.^[1]

Is copper sulfate safe for a septic tank?

The label says 2 pounds added to an active 300-gallon septic tank temporarily reduces bacterial action, which returns to normal about 15 days after treatment. It isn't for sale or use in septic systems in Florida, Massachusetts and Washington.^[1]

How often can I treat a sewer line?

No more than twice a calendar year, at least 6 months apart, with no more than 2 pounds per treatment. The label suggests spring after plant growth begins or late summer to early fall.^[1]

Can I use it in a koi or goldfish pond?

Be very careful. NPIC says trout, koi and juvenile fish are particularly sensitive to copper, and that fish kills after algae treatments have mostly been blamed on oxygen depletion and debris. The label's limits are at least 14 days between treatments and no more than half the water area at a time.^[3][1]

Sources

1. U.S. EPA Pesticide Product Label System, “Copper Sulfate Crystals label, EPA Reg. No. 56576-1 (EPA-stamped, February 4, 2022).” www3.epa.gov/pesticides/chem_search/ppls/056576-00001-20220204.pdf (accessed 2026-11-08)
2. U.S. EPA Pesticide Product Label System, “Roebic K-77 Root Killer label, EPA Reg. No. 7792-1 (EPA-stamped, August 14, 2020).” www3.epa.gov/pesticides/chem_search/ppls/007792-00001-20200814.pdf (accessed 2026-11-08)
3. National Pesticide Information Center, “Copper Sulfate General Fact Sheet (reviewed November 2012).” npic.orst.edu/factsheets/cuso4gen.html (accessed 2026-11-08)
4. National Pesticide Information Center, “Copper Sulfate Technical Fact Sheet (reviewed December 2012).” npic.orst.edu/factsheets/archive/cuso4tech.html (accessed 2026-11-08)
5. Fungicide Resistance Action Committee, “FRAC Code List 2025.” www.frac.info/media/ljsi3qrv/frac-code-list-2025.pdf (accessed 2026-11-08)
6. Roebic Laboratories, Inc., “Roebic K-77 Root Killer Safety Data Sheet (Roebic Laboratories, issued and revised May 22, 2015; EPA Reg. No. 7792-1).” roebic.com/wp-content/uploads/2024/02/K-77_Root_Killer_SDS.pdf (accessed 2026-11-08)