There are a large amount of industrial wastewater during manufacturing of printed circuit boards, which is one of the sources of water pollution. Once the wastewater seeps into the ground, and is discharged into water bodies, it not only harms the environment, but also causes serious pollution to water bodies. It endangers our health and the development of industry, agriculture, and fisheries.

1. Suspended substance

The industrial wastewater during PCB manufacturing contains organic and inorganic suspended solids. These things discharge into water body, makes it darker color. The organic matter will decay and decompose, giving off an unpleasant smell. At the same time, it will consume lots of oxygen in water, endangering the survival of fish and shellfish.

2. Cyanide

Cyanide-containing wastewater mainly comes from processes such as electroplating gold. Cyanide is extremely toxic. It can accumulate in our body and cause poisoning. Humans will die if they consume 0.1g of sodium cyanide. It's even more toxic to fish. When the cyanide concentration reaches 0. 04-0. 1 mg/L, fish will die.

3. Acid and alkaline wastewater

Acid and alkali wastewater is a common during manufacturing. If there are only hydroxyl ions or hydrogen ions in the wastewater, hazards are reduced, but it cannot be ignored. In fact, it harms the survival of microorganisms in water, and microorganisms play an important role in purifying water quality.

When wastewater is discharged into farmland, it will destroy the soil's aggregate structure, affect soil fertility, air permeability, water storage, etc., and directly harm the growth of crops. For example, the acid-base wastewater consumed by fish, livestock, etc. directly pollutes meat and milk, endangers human health.

4. Heavy metals

Chromium

Chromium pollution mainly comes from backward technology. Chromium compounds can cause many types of damage to human body, including systemic poisoning, dermatitis, eczema, and allergic reactions due to skin contact. Hexavalent chromium is the most toxic and carcinogenic. Laws and regulations stipulate that harmful substances in electronic products are restricted, so chromium is no longer used in manufacturing of printed circuit boards.

Pb

Pb comes from electroplating tin-lead alloy and related processes of removing tin-lead after cleaning and etching, as well as lead vapor during hot air leveling. Lead and its compounds are toxic. The toxicity varies depending on the solubility of the lead compound in liquid, the particle size of the lead compound, and form of the compound. Lead enters human body, it's not easily excreted. It has toxic effects on various tissues, among which the lesions of nervous system, hematopoietic system and blood vessels are obvious.

If the human body absorbs more than 1 mg of Pb per day, it accumulates significantly, leading to chronic poisoning over a long period of time. The poison invades the human body through the respiratory tract or contaminates food and water, then invades the human body through the digestive system. It's first accumulated in the bone marrow, liver, brain and bones, and then slowly released, enters blood, and accumulates in soft tissues, causing toxic effects. Pb also harms fish. Lead nitrate is the most toxic to fish. When the concentration is 0. 1mg/L, it can kill fish.

Cu

Copper is the most used heavy metal in PCB manufacturing. When excessive Cu enters human body, symptoms such as headache, dizziness, general weakness, metallic taste in the mouth, nausea, vomiting, and abdominal pain may occur. The lethal dose of Cu for humans is about 10g. Easily soluble copper compounds are particularly toxic to fish. It is believed that when the concentration of copper compounds in water reaches 0. 002mg/L, it will begin to have a lethal effect on fish.

Nickel

Nickel pollution mainly comes from nickel plating and its cleaning water. After nickel enters human body, it mainly exists in the spinal cord, brain, lungs and heart, mainly lungs. If a large amount of nickel salt is accidentally taken, acute gastrointestinal irritation may occur, resulting in vomiting and diarrhea. Metal nickel powder and nickel compounds may cause tumors in animals, and the lungs may gradually harden. The poison of nickel and its salts to operators mainly causes nickel dermatitis.

Sulfide

Sulfide refers to hydrogen sulfide and its salts such as sodium sulfide, which mainly come from photographic platemaking and micro-etching with ammonium persulfate. Sulfide is not toxic to humans and animals, but it can worsen people's sensory state. Sulfide in water is easily oxidized to sulfate or thiosulfate, which consumes oxygen dissolved in water. It affects the normal survival of aquatic organisms.

Formaldehyde

Formaldehyde is used as a reducing agent in the chemical copper deposition process. It's in gas and cleaning water. The direct toxicity of formaldehyde is low, but it is also a carcinogen and irritates the human respiratory system. It will make the water smelly and pollute air.