Environmental Engineering Reference
In-Depth Information
(continued)
Constituent
Maximum Concentrations
for Irrigation (mg/L)
Remarks
Beryllium
0.10
Toxicity to plants varies widely, ranging from
5 mg/L for kale to 0.5 mg/L for bush beans
Boron
0.75
Essential to plant growth; suf
cient quantities
in reclaimed water to correct soil de
ciencies.
Optimum yields obtained at few-tenths mg/L;
toxic to sensitive plants (e.g. citrus) at 1 mg/L.
Most grasses are tolerant at 2.0 -10 mg/L
Cadmium
0 01
Toxic to beans, beets, and turnips at concen-
trations as low as 0.1 mg/L; conservative limits
are recommended
Chromium
0.1
Not generally recognized as an essential ele-
ment; due to lack of toxicity data, conservative
limits are recommended
Cobalt
0.05
Toxic to tomatoes at 0.1 mg/L; tends to be
inactivated by neutral and alkaline soils
Copper
0.2
Toxic to a number of plants at 0.1 to 1.0 mg/L
Fluoride
1.0
Inactivated by neutral and alkaline soils
Iron
5.0
Not toxic in aerated soils, but can contribute to
soil acidification and loss of phosphorus and
molybdenum
Lead
5.0
Can inhibit plant cell growth at very high
concentrations
Lithium
2.5
Tolerated by most crops up to 5 mg/L; mobile
in soil. Toxic to citrus at low doses- recom-
mended limit is 0.075 mg/L
Manganese
0.2
Toxic to a number of crops at few-tenths to few
mg/L in acidic soils
Molybdenum
0.01
Nontoxic to plants; can be toxic to livestock if
forage is grown in soils with high molybdenum
Nickel
0.2
Toxic to a number of plants at 0.5 to 1.0 mg/L;
reduced toxicity at neutral or alkaline pH
Selenium
0.02
Toxic to plants at low concentrations and to
livestock if forage is grown in soils with low
levels of selenium
Tin, Tung-
sten, and
Titanium
-
Excluded by plants; specific tolerance levels
unknown
Vanadium
0.1
Toxic to many plants at relatively low
concentrations
Zinc
2.0
Toxic to many plants at widely varying
concentrations; reduced toxicity at increased
pH (6 or above) and in
fine-textured or organic
soils
Source: USEPA (
2012
: 3-9)
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