According to the control standards for pollutants in farmland sludge in China (GB484-84), the maximum allowable concentrations of heavy metals and compounds are clearly stipulated. For example, the concentration of mercury and its compounds (based on Hg) is 5 mg/kg for acid soil and 20 mg/kg for neutral soil and alkaline soil. The concentration of other heavy metals, e.g. cadmium, chromium, arsenium, lead and boron, mineral oil, benzopyrene, copper and its compounds, zinc and its compounds, nickel and its compounds, etc. are all clearly defined. According to the control standards for municipal waste for farmland use (GB172-87), the concentration of impurities, particle sizes, mortality of ascarid eggs, the value of fecal coliform bacteria, total mercury, total cadmium, total lead, total chromium, arsenium, organic matter, total nitrogen, total phosphor, total potassium, pH, moisture, etc. are all clearly stipulated, which will not be listed here one by one.
Here, I can promise the three inflexible standards of artificial soil, i.e. 1) heavy metal content controlled below 1 ppm; 2) content of hazardous substances (such as pesticide residues, toxic compounds and radioactive materials) reduced to almost zero; and 3) the content of organic matter controlled at 5%-10%.