Table 2.
Summary of the characteristics of the trace elements used in the Heavy Metal Index (HMI), primarily from information reported in Alloway (2013)
| Element | Primary anthropogenic associations | Examples of specific anthropogenic sources | Published natural background concentration (ppm) | Background concentration threshold (ppm) |
|---|---|---|---|---|
| Silver (Ag) | Industry |
• Various industrial operations • Nanoparticle contamination |
0.05–1.00 | 1.0 |
| Cadmium (Cd) | Agriculture |
• Phosphate fertilizers • Iron and steel production • Oil combustion |
0.1–1.0 | 1.0 |
| Cobalt (Co) | Industry | • Industrial application of oxides, hydrous oxides, or arsenides | < 50 | 25 |
| Chromium (Cr) | Industry/agriculture |
• Stainless steel production • Sewage sludge • Fly ash • Slag |
0.5–250 | 125 |
| Copper (Cu) | Agriculture/industry/roads |
• Manure • Sewage sludge • Phosphate fertilizers • Agricultural pesticides • Atmospheric deposition from volcanic eruptions, forest fires, sea-salt spray • Metal production • Fossil fuel combustion • Brake and tire wear from cars and railroads |
2–50 | 50 |
| Nickel (Ni) | Industry/agriculture |
• Metal-processing emissions • Coal/oil combustion • Sewage sludge • Phosphate fertilizers |
0.2–450 | 225 |
| Lead (Pb) | Roads/industry |
• Leaded gasoline • Smelting of base ores • Ammunition • Sewage sludge |
Mean of 17a | 35 |
| Antimony (Sb) | Industry |
• Smelting of base ores • Flame retardant and catalyst in plastics • Ammunition |
0.1–1.9 | 1.0 |
| Tin (Sn) | Industry/agriculture |
• Marine antifouling paints • Agricultural pesticides • Industrial fungicides • Slimicides • Wood preservatives |
1.7–50 | 17 |
| Vanadium (V) | Industry/roads |
• Coal/oil combustion • Petroleum products |
36–150 | 150 |
| Tungsten (W) | Industry/agriculture |
• Mining • Various industrial operations • Military operations • Ammunition • Household waste disposal (e.g., lightbulbs) |
< 2 | 2.0 |
| Zinc (Zn) | Industry/agriculture |
• Fossil fuel combustion • Atmospheric deposition from volcanic eruptions, forest fires • Inorganic fertilizers • Manure • Sewage sludge |
10–150 | 150 |
Background concentration thresholds are based on the published natural background concentrations and adjusted for consistency with natural breaks in our data (see Fig. 4). Thresholds are used to reflect human-mediated additions of heavy metals to wetland soils
aAlloway (2013) publishes a global mean for Pb, reported in this table, which is consistent with means determined for the conterminous US by Shacklette and Boerngen (1984)