Commercial phosphate (P) fertilizers contain small amounts of heavy-metal contaminants which were minor
constituents in phosphate rock (PR). Animal manures and sewage sludges (biosolids) are the main organic fertilizers
and the latter also may contain heavy-metal contaminants. Heavy metals in biosolids may be found in the inorganic
form or may be organically complexed, which could affect their chemical reactions in soil. These heavy metals may
accumulate in soft with repeated fertilizer applications. Cadmium (Cd) is the heavy metal of most concern because
it may affect human health. Other heavy metals of possible significance are arsenic (As), chromium (Cr), lead (Pb),
mercury (Hg), nickel (Ni), and vanadium (V). Some countries have set tolerance limits on heavy-metal additions
to soil because their long-term effects are unknown. These limits usually are set for the tillage layer (surface 20-30
cm) of soil where most root activity occurs. Controls on heavy-metal concentrations in sewage biosolids and their
maximum total and annual loading rates to soil have been imposed in some countries. Regulations also have been
proposed for phased-in limits on maximum heavy metal concentrations permitted in P fertilizers, or they are already
in effect. Most of the fertilizer regulations relate Cd limits to P concentrations, so P application rates dictate Cd
inputs to soil. Regulations affecting sewage biosolids include a number of heavy metals, while those concerning P
fertilizers only include limits on Cd at this time.
Increased concern about the entry of various heavy
Commercial phosphate (P) fertilizers contain small amounts of heavy-metal contaminants which were minor
constituents in phosphate rock (PR). Animal manures and sewage sludges (biosolids) are the main organic fertilizers
and the latter also may contain heavy-metal contaminants. Heavy metals in biosolids may be found in the inorganic
form or may be organically complexed, which could affect their chemical reactions in soil. These heavy metals may
accumulate in soft with repeated fertilizer applications. Cadmium (Cd) is the heavy metal of most concern because
it may affect human health. Other heavy metals of possible significance are arsenic (As), chromium (Cr), lead (Pb),
mercury (Hg), nickel (Ni), and vanadium (V). Some countries have set tolerance limits on heavy-metal additions
to soil because their long-term effects are unknown. These limits usually are set for the tillage layer (surface 20-30
cm) of soil where most root activity occurs. Controls on heavy-metal concentrations in sewage biosolids and their
maximum total and annual loading rates to soil have been imposed in some countries. Regulations also have been
proposed for phased-in limits on maximum heavy metal concentrations permitted in P fertilizers, or they are already
in effect. Most of the fertilizer regulations relate Cd limits to P concentrations, so P application rates dictate Cd
inputs to soil. Regulations affecting sewage biosolids include a number of heavy metals, while those concerning P
fertilizers only include limits on Cd at this time.
Increased concern about the entry of various heavy
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