Hazards of Hydrogen Sulfide and Its Treatment and Prevention

2026-06-05

I. Hazards of Hydrogen Sulfide in Water Bodies:

Hydrogen sulfide (H₂S) is a soluble, toxic gas with the characteristic odor of rotten eggs. In aquaculture systems, concentrations as low as 0.2 mg/L can induce feeding inhibition in healthy fish, while levels exceeding 0.5 mg/L can lead to mass mortality. In shrimp and crab hatchery waters, its harmful effects are particularly severe; even at 0.2 mg/L, H₂S can cause mild mortality. Studies on the mechanisms of H₂S toxicity in crustaceans have shown that it disrupts both central and peripheral nervous systems, impairing locomotion and balance. Additionally, H₂S can bind to hemocyanin in shrimp blood, reducing its oxygen‑binding affinity and resulting in hypoxic symptoms.

II. The methods for determining whether hydrogen sulfide levels exceed the threshold primarily include the following aspects:

1. Biological reaction:

Fish, shrimp, crabs, and other cultured species are heavily concentrated in the upper water column, exhibiting physiological avoidance of the lower layers. Some also display anorexia, restlessness, and erratic swimming near the surface; many escape from ponds or leap out of the water, with gills turning black and swimming legs and walking legs first yellowing then blackening. In severe cases, mass mortality occurs.

2. Odor assessment:

Hydrogen sulfide has a strong rotten-egg odor; if you detect this smell downwind, and the odor intensifies when the aerator is turned on, it may indicate that hydrogen sulfide levels have exceeded the permissible threshold.

3. Sediment color and odor:

The sediment at Tangkou is black, and the water emits a foul odor reminiscent of rotten eggs—both are clear indicators of elevated hydrogen sulfide levels.

4. Testing

Collect water samples containing bottom sediments and perform bacterial enumeration on TCBS agar plates; Vibrio species will form green or yellow colonies, while sulfate-reducing bacteria will produce black colonies. Alternatively, use a hydrogen sulfide detection reagent.

In aquaculture, the production of hydrogen sulfide is primarily associated with the following factors:
In aquaculture systems, residual feed, feces, and the remains of dead organisms are rich in nutrients such as proteins, lipids, and carbohydrates, providing an abundant substrate for microbial proliferation. When the oxygen consumption rate exceeds the reaeration rate and hydrodynamic conditions are inadequate, anaerobic microorganisms can degrade sulfur‑containing proteins, producing large quantities of malodorous gases like hydrogen sulfide and ammonia.
Seawater, soil and rock formations, as well as rainwater and groundwater in areas with high-sulfur coal combustion, contain substantial amounts of sulfate, which under anaerobic conditions is reduced to hydrogen sulfide.

III. Prevention and Control of Hydrogen Sulfide:

1. Increase dissolved oxygen: Hydrogen sulfide tends to accumulate under low-oxygen conditions; therefore, by using aerators and oxygen tablets to boost the oxygen levels in the water, you can inhibit the growth and reproduction of anaerobic bacteria, thereby reducing hydrogen sulfide production.

Bottom-conditioning: Sulfates and organic sulfur compounds in pond sediments serve as precursors to hydrogen sulfide. Reducing these substances in the pond bottom can effectively curb H₂S production. Using a powerful bottom-conditioning agent, highly oxidizing nascent ozone is rapidly released into the water, swiftly oxidizing the pond bottom, suppressing harmful microorganisms in both the water column and the sediment, and alleviating undesirable conditions such as blackened, malodorous, or thermally heated bottoms. Additionally, regularly remove excess accumulated sludge from the pond.

Before use:

After use:

3. Adjusting the water’s pH: Disinfection with quicklime raises the water’s pH, thereby reducing the toxic effects of hydrogen sulfide; however, care must be taken to avoid excessively high pH levels that could lead to ammonia toxicity.

4. Reduce the sources of sulfur in the water: By feeding fish with scientifically formulated diets, minimize the accumulation of organic matter in the water, thereby decreasing the likelihood of hydrogen sulfide formation.

Water conditioning: Use Zhongren Ultra-Concentrated Sulfur-Oxidizing Bacteria, a highly efficient, fast-sinking strain that rapidly degrades sulfides, preventing their accumulation in the environment. This helps to aerate and break down bottom sludge, eliminate foul odors at the pond bottom, and enhance the self‑purification capacity of the sediment. With long-term application, it can effectively improve the color and odor of bottom sediments and efficiently control and eliminate hydrogen sulfide problems in aquaculture.