使用原子吸收光谱法测定土壤中的铅

Lead does not biodegrade and remains in soil indefinitely, posing serious health risks. Children are particularly vulnerable, experiencing developmental delays, learning disabilities, and brain damage from exposure. Plants grown in contaminated soil absorb lead, which can be ingested through vegetables and herbs, while contaminated soil particles can be inhaled or tracked indoors.

The Environmental Protection Agency set a limit of 400 ppm for lead in gardening and play areas, and 1,200 ppm in other areas. Soils exceeding 400 ppm should not be used for gardening. Between 100-400 ppm, leafy vegetables and herbs should be avoided due to lead accumulation in leaves, and root vegetables should not be grown.

Atomic absorption spectroscopy uses a hollow cathode lamp to emit light at a specific wavelength. Sample atoms absorb this light, exciting electrons to higher energy states. The amount of light absorbed is proportional to element concentration. A standard curve created from known concentrations determines the unknown sample concentration, providing quantitative data for at least 50 elements.

Soil samples are collected using a soil auger, then sieved to remove large chunks and dried at 40°C for 24 hours. One gram is weighed and digested in concentrated nitric acid and water in a block digester. Hydrogen peroxide is added to oxidize organic matter, followed by hydrochloric acid. The final solution is filtered and diluted to 100 mL for AAS analysis.

Atomic absorption spectroscopy can detect mercury in seafood, pesticide residues like monosodium methyl arsenate in soil layers, and multiple metals in drinking water including zinc, copper, nickel, cadmium, and manganese. The technique measures total elemental concentration regardless of chemical form, making it versatile for environmental monitoring across soil, water, and food samples.

Lead occurs naturally in soils at levels ranging from 10 to 50 parts per million. However, widespread use of lead in paint and gasoline, combined with industrial contamination, has elevated urban soil concentrations significantly above background levels, sometimes reaching 10,000 ppm in heavily contaminated areas.

Atomic absorption spectroscopy can detect concentrations as low as parts per billion for some elements, though measurement ranges of parts per million are most common for metals like lead. This sensitivity allows detection of trace contamination in environmental samples, including drinking water with lead levels below 2 ppb, well within EPA safety limits.