Cadmium in Plants

GEOLOGICAL SURVEY BULLETIN 1314-G

I/Q -

lui

Cadmium in Plants

By HANSFORD T. SHACKLETTE

CONTRIBUTIONS TO GEOCHEMISTRY

GEOLOGICAL SURVEY BULLETIN 1314-G

An account of the concentrations of cadmium 

in plants from areas that have normal or 

anomalous amounts of this element 

in the air or soil

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 72-600270

For sale by the Superintendent of Documents, U.S. Government

Printing Office, Washington, D.C. 20402 - Price 40 cents

Stock Number 2401-00251
CONTENTS

Page

Abstract..........-.... ........-.. ............................................................................ Gl

Introduction.....-..................................---.....-......-............. ..............------. . - 1

Experiments in cadmium absorption by plants.. .......................................... 2

Cadmium concentrations in plants.-.......---........-----------.---------.-----.--.....---- 3

Standard plant samples.................................................. . .. .......... 3

Environments that have common levels of cadmium............. .............. 4

Environments that have uncommonly high levels of cadmium............. 8

Naturally occurring cadmium concentrations-.------.-----.-----.---. 8

Cadmium from vehicular, industrial, and urban pollution............ 10

Airborne cadmium measured by analysis of Spanish moss.-...--,-.-.... 16

Discussion and summary..................... ............................................. ...... 22

Conclusions...... ........ ..... ....... ......-......- .-....... -- - 24

References cited.....--..................................----.--.-.....--..................-....... ... 25

ILLUSTRATIONS

Page

FIGURE 1. Map showing localities of Spanish moss samples, and cadmium concentrations in these samples-.......................-..... ..... G18

2. Map showing localities of Spanish moss samples, and ash

content of the samples.........-----......................-........ ............. 21

TABLES

Page

TABLE 1. Mean cadmium concentrations in tree, shrub, and grass samples from six vegetation-type areas in Missouri...................... G7

2. Mean cadmium concentrations and ash yields in tree and

shrub samples from mineralized areas in Colorado.............. 10

3. Estimates of cadmium concentrations in some plants and

plant parts....................................................................................... 24

in

CONTRIBUTIONS TO GEOCHEMISTRY

CADMIUM IN PLANTS

By HANSFORD T. SHACKLETTE

ABSTRACT

Cadmium in low concentrations most likely is a normal constituent of all 

plant tissues. The concentration in the tissue is determined by the inherent 

ability of a plant species to absorb cadmium and by the cadmium concentration in the environment. Differences in cadmium content among plants of 

different species growing in low-cadmium soils commonly are greater than 

differences in amounts of cadmium in the soils. The cadmium content of plant 

tissue tends to increase with increase of concentrations of soil cadmium above 

certain background amounts. Airborne cadmium, originating in emissions 

from the combustion of hydrocarbons or from certain industrial processes, 

may enter the soil and be absorbed by plants or may be deposited on the surface of plants in particulate matter until very high levels of cadmium are 

accumulated by the plants. Spanish moss, a plant with no connection to the 

soil, seems to be a useful indicator of the relative extent of airborne cadmium 

pollution, in that it contains much more cadmium if growing in areas where 

aerial pollution is likely than if growing in areas remote from sources of 

pollution. There seems to be no natural means by which cadmium is eliminated from plant tissue, and no cultural practice has been found to be effective in reducing or preventing the absorption of cadmium by plants.

INTRODUCTION

Cadmium has been found in many plant species and plant organs, although it is not usually considered to be an essential micronutrient. However, it has been reported to increase the sugar 

content and yield of grapes when applied in a foliar spray (Dobrolyubskii, 1957; Dobrolyubskii and Slavvo, 1958) and to increase 

the yield of red clover when applied in combination with boron 

(Dmitriev, 1939). Bertrand and de Wolf (1959) stated that in the 

fungus Aspergillus nic/er, cadmium may substitute for zinc in the 

synthesis of tryptophane, an amino acid necessary for the elaboration of indoleacetic acid hormone.

The concentrations of cadmium that are toxic to plants are 

largely unknown. High levels of zinc often accompany anomalous 

amounts of cadmium in the environment, and both elements may 

simultaneously exert a toxic effect at the same time. UlrychovaGl
G2 CONTRIBUTIONS TO GEOCHEMISTRY

Zelinkova (1959, p. 139) stated that "All authors agree that cadmium ions are definitely more poisonous [to plants] than zinc 

ions." She (1959) reported further that doses greater than 160 

milligrams cadmium per plant nearly halved the inorganic phosphorus content of tobacco plants (Nicotiana tabacum Samsun) 

and produced necrotic spots on the leaves, and she suggested that 

cadmium disturbs phosphorus metabolism.

Soon after McMurtrey and Robinson (1938, p. 817) had stated 

that "It [cadmium] is one of the very few elements that have not 

been reported in plants," Clemente and Mendez (1940) detected 

cadmium in cabbage (Brassica oleracea L.), potato (Solanum tuberosum L.), sweet potato (Ipomea batatas L.), lettuce (Lactuca 

sativa L.), green pepper (Capsicum frutescens L.), and tomato 

(Lycopersicnm escidentum Mill.), but they did not report the concentrations. Later analyses of plant materials by more sensitive 

methods have indicated that this element is present in measurable 

concentrations in all plant tissues.

EXPERIMENTS IN CADMIUM ABSORPTION BY PLANTS

Cadmium is readily absorbed by soil-rooted plants from solutions of cadmium compounds applied to the soil. Autoradiographic 

studies by Gordee, Porter, and Langston (1960) indicated that 

exposure of peppermint (Mentha piperita L.) plants to radioactive cadmium in soil resulted in the uptake of the element after 

24 hours and in its gradual movement through the vascular system to all parts of the plant, with the greatest accumulation occurring in the lower leaves. They reported that cadmium was not 

eliminated by the plant following leaching of the soil.

In experiments with radish (Raphanus sativus L.) designed to 

test the possibility of preventing or impeding cadmium accumulation in food plants by the interactive effect of zinc, Lagerwerff 

and Biersdorf (1972) combined 2, 20, and 100 ppb (parts per billion) cadmium and 20, 100, and 400 ppb zinc in culture solutions. 

At the lowest concentration of cadmium, increasing the concentrations of zinc suppressed cadmium uptake; but at the 100-ppb level 

of cadmium, increasing amounts of zinc increased cadmium uptake. The great reduction in crop yield caused by levels of zinc 

that were effective in suppressing cadmium absorption, together 

with the failure of zinc to inhibit cadmium uptake at high levels 

of both elements, limits the practical possibilities of reducing cadmium levels in plants by applying zinc to the soil.

Dr. W. H. Alloway, of the U.S. Plant, Soil, and Nutrition Laboratory, reported (written commun., 1971) that in experiments 

conducted at this laboratory increasing the levels of zinc in culture 

solutions did not depress the uptake of cadmium by plants.
CADMIUM IN PLANTS G3

Schroeder and Balassa (1963) conducted field-plot experiments 

to determine if the cadmium in superphosphate fertilizers could 

be absorbed in detectable amounts by food and feed plants. They 

reported that adding 20-percent superphosphate containing 

7.25 ppm (parts per million) cadmium to soil increased the cadmium content of 10 garden vegetables from nondetectable levels in 

control plots to 0.3-4.0 ppm (wet-weight basis) in the treated 

plots. Parsnip (Pastinaca sativa L.) appeared to be a cadmium 

accumulator that in the control plot contained 3 ppm cadmium, 

and in the superphosphate-treated plot, 14.0 ppm.

In a study of the influence of soil type on the mineral composition of corn (Zea mays L.), Prince (1957) found the cadmium 

content of dry material of mature plants from four different types 

of soil to range from 0.81 to 2.43 ppm, but he did not give the cadmium concentrations in the soils. He reported average values of 

1 ppm cadmium in mature corn leaves, 0.96 ppm in the dry grains, 

and 0.67 ppm in the husks. Ragweed (Ambrosia artemisiifolia L.) 

that grew with the corn averaged 0.46 ppm cadmium.

Schroeder, Nason, Tipton, and Balassa (1967, p. 195) stated:

Because superphosphate fertilizers contain cadmium, experiments designed to 

ascertain the uptakes by growing vegetables heavily fertilized with 20 percent 

superphosphate were repeated. The grains so fertilized had more cadmium 

than did their controls, as did two legumes, three root vegetables, four leafy 

vegetables, three fruits, and one squash. Mean differences were not impressive.

In experiments designed to determine if cadmium was translocated from tree leaves to the fruit, Ross and Steward (1969) 

sprayed apple trees with an aqueous solution of cadmium chloride 

containing 43 ppm cadmium. They reported (1969, p. 52) :

The results presented here show that following cover sprays of cadmium 

chloride, cadmium accumulates in apple fruit as it matures. The form in 

which cadmium is translocated is not known. Cadmium residues persist in the 

foliage throughout the growing season * * * the cadmium may be translocated 

from the foliage to the fruit.

CADMIUM CONCENTRATIONS IN PLANTS 

STANDARD PLANT SAMPLES

For use in the comparison of the accuracy and precision of 

analytical methods used for plant analysis, several laboratories 

have prepared "standard plant samples" for distribution to other 

laboratories. In 1963, U.S. Geological Survey personnel collected 

four "standard alfalfa" (Medicago sativa L.) samples in Arizona 

and one in Utah that have been widely used for comparing analytical methods. The cadmium concentrations, in parts per million of 

ash, the ash yield, as a percentage of dry weight, and the calculated cadmium concentrations, in parts per million, of the dry
G4 CONTRIBUTIONS TO GEOCHEMISTRY

material are given in the table below (analyses by T. F. Harms, 

using an atomic-absorption method).

Analyses of standard samples

Calculated

Sample ., . , T . Cadmium in Ash yield cadmium 

No. V;irlet y Location ash(ppm , (percent) in dry

plants (ppm I 

A-l Common mixed Graham County, Ariz., 0.3 11.5 0.035

near Safford. 

A-2 Hairy Peruvian and Pima County, Ariz., .3 11.2 .034

Chilean mixed. near Tucson.

A-3 "919". . . . do . .2 10.7 .021 

A-4 (Unknown). Pinal County, Ariz., 15 .3 10.5 .032

miles south of Mesa.

A-5 I Unknown I Millard County, Utah, .3 8.5 .026

near Delta.

A "standard kale" sample, consisting of dried pulverized leaves 

of kale (Brassica olcracea var. acephala DC.), was prepared by 

Bowen (1967a) and distributed for analysis to 29 cooperating 

laboratories. Analyses by polarographic methods indicated a mean 

value of 1.0±0.1 ppm in the dry material (Bowen, 1967a), and 

analyses by neutron-activation methods gave a mean value of 

0.384 ppm (Bowen, 1967b).

The U.S. National Bureau of Standards recently issued a series 

of Biological Standard Reference Materials (Becker and LaFleur, 

1972). The plant sample in the series consists of dried pulverized 

"orchard leaves" from several kinds of fruit-bearing plants. Analyses by atomic-absorption spectroscopy and polarography by the 

Analytical Chemistry Division of the Bureau of Standards indicated Q.ll±Q.Q2 ppm cadmium in the dry leaves.

ENVIRONMENTS THAT HAVE COMMON LEVELS OF CADMIUM

The mean cadmium concentration in the ash of "surface" plants 

was reported by Malyuga (1964, p. 15) to be 1 10" percent 

(0.01 ppm). This value seems to be much too low for cadmium in 

plant ash but would be a reasonable value (although still low) for 

the concentration of cadmium in the dry plant material. Earlier, 

Malyuga (1941) gave cadmium concentrations in dry weight of 

plant material that seem entirely possible (see the paragraph that 

follows) ; therefore, his average value of 0.01 ppm in plant ash is 

believed to be erroneous. No other investigator is known to have 

attempted to give an "average" value for cadmium concentration 

in plants.

The average cadmium concentration in sea water was stated by 

Goldberg (1965, p. 164) to be 0.00011 /ig'1 (micrograms per liter) 

(about 0.11 ppb). Malyuga (1941) reported cadmium concentrations, as parts per million of dry weight, in marine algae, a marine 

flowering plant, and aspen bark, as follows:

Marine algae: Allaria esculenta, 1 ppm; Ascophyllum nodosum, 0.29 ppm; FUCKS in flat us, 0.16 ppm; Fucns serratns,
CADMIUM IN PLANTS G5

0.34 ppm; Laminaria saccharina, 0.14 ppm; and Phyllar'm dennatodea, 0.1 ppm.

Marine flowering plant: Zostera marina, 0.23 ppm. 

Tree (aspen) bark: Populns tremula, 1.6 ppm.

Ishibashi, Fujinaga, Morii, Kanchiku, and Kamiyama (1964) 

analyzed samples of marine algae by the dithizone extraction and 

polarographic method and reported the cadmium concentrations, 

in parts per million, of the dried samples as follows: Acanthopeltis 

japonica, 0.1; Desmarestia viridis, 0.1; Eisenia bicyclis, 0.3; Gelidium sp., 0.2; and Ulva sp., 0.2.

The range of concentrations, in parts per million, of cadmium 

in some dry plant materials that presumably were produced on 

soil of normal cadmium content was given by Shirley, Benne, and 

Miller (1949, p. 303) as follows: Dried spinach, 0.6-1.2; dried 

lettuce, 0.3-0.5; and alfalfa-leaf meal, 0.1-0.2.

Analyses of the cadmium concentrations in a wide variety of 

plants and plant products were given by Schroeder, Nason, Tipton, 

and Balassa (1967). The values were reported in micrograms per 

gram (//g/gr^ppm), based on the "wet" weight of the materials. 

The losses in weight in drying and ashing the samples were not 

given; therefore, the reported values cannot be converted to dryweight or ash-weight bases. These authors reported the following 

ranges in cadmium concentrations in "wet" plant material (^g/g) : 

Leaves of trees and shrubs, 0.04-0.49; fern leaves, 0.04-0.33; 

fungi, 0.10-1.95; grains, 0.04-0.49; and nuts, 0.04-0.07.

Kropf and Geldmacher-von Mallinckrodt (1968) reported the 

cadmium concentrations that they found in samples of fruits, vegetables, and grains, as well as in many other kinds of foods. Cadmium concentrations in samples of the edible parts of the food 

plants averaged 0.075 ppm, with a low value of 0.004 and a high 

value of 282 ppm. These values cannot be compared in any way 

with the data in table 3 of the present report because they are 

based on the wet weights of the foods. These foods are known to 

differ greatly in water content, but this content was not given for 

the samples. Average wet-weight cadmium values derived from 

analyses of foods as different in water content as fresh tomatoes 

(probably 95 percent water) and dried beans (probably about 5 

percent water) may be useful in estimating dietary intake of 

cadmium, but they have little usefulness in characterizing the 

cadmium concentrations in different foods because of the widely 

fluctuating water content of the foods.

The leaves of 12 species of trees and shrubs were analyzed for 

cadmium and other elements by Hanna and Grant (1962). These 

plants grew in Nixon sandy loam or in Quakertown silt loam, and 

the cadmium concentrations are presumed to be normal, although

479-610 O - 72 - 2
G6 CONTRIBUTIONS TO GEOCHEMISTRY

cadmium levels in the soils were not given. The dried leaf samples 

were digested with nitric and perchloric acids, then analyzed by 

a spectrochemical method. The cadmium concentrations in the 

samples, in parts per million of dry weight, are summarized as 

follows: Acer rubrum (red maple), 1.7 (average of four samples) ; 

Acer saccharinum (silver maple), 0.10; Acer saccharum (sugar 

maple), 0.21; Ilex opaca (American holly), 5.2 (average of four 

samples) ; Kalmia latifolia (mountain laurel), 0.43 (average of 

two samples) ; Pieris japonica, 1.2 (average of five samples) ; 

Pinus strobus (white pine), 0.9 (average of three samples) ; 

Quercus palustris (pin oak), 2.4 (average of four samples) ; and 

Tsuga canadensis (Canadian hemlock), 0.6 (average of two samples). Hanna and Grant (1962, p. 293) wrote: "Statistical analyses of these data [for 23 elements] indicate more differences in 

composition between species growing in the same soil than between 

plants of the same species growing in different soils."

A U.S. Geological Survey study of geochemical environments in 

Missouri included sampling of plants and soils in six vegetationtype areas (as mapped by Kiichler, 1964, but somewhat modified). 

The specific sampling sites were selected to avoid areas of major 

industrial and vehicular pollution. All samples of soils at 300 sites 

in these areas contained less than 1 ppm cadmium. These sites 

were, therefore, considered to have only the typically low concentrations of cadmium in the soils and the atmosphere. The terminal 

6- to 8-inch part of stems (branches) of trees and shrubs that are 

characteristic species of the vegetation types at the sites, plus a 

species of grass at three sites, were sampled and analyzed for ash 

yield (C. S. E. Papp, analyst) and for concentrations of various 

elements. Results of the cadmium analyses (T. F. Harms, analyst) 

are given in table 1.

Concentrations of cadmium were determined by analysis of the 

ash of plant samples, as given in table 1, and they were also converted to approximate concentrations in the dry samples as needed 

for comparisons with the literature which uses dry weight as the 

basis for reporting concentrations by the following equation:

Cadmium (ppm) in dry plant

, . , . . , ash content (percent) = cadmium (ppm) in ash X TTTTJ - 

The geometric means and geometric deviations given in table 1 

are antilogs, respectively, of the arithmetic means and standard 

deviations of the logarithms of the analytical values. The geometric mean is a measure of central tendency of the frequency 

distribution and, as such, is an estimate of the typical or most 

common concentration for the element. The arithmetic means of
TABLE 1. Mean cadmium concentrations in tree, shrub, and grass samples fr

[n, number of samples ; AM, arithmetic mean ; GM, geometric mean ; GD, geomet

Common and scientific name

Big bluestem grass (Andropofjon gerardii 

Vitman) . 

Buckbush (Symvhoricarpos orbiculatus 

Moench) .

Shagbark hickory (Carya ovata (Mill.) 

K. Koch).

Winged sumac (Rhus copallina li.) .................

Plant part

Stem and 

leaf. 

Stem .. ... .

.......... do........

.Stem and 

leaf.

Stem .......

leaf.

....... ....do..........

...... .....do...... ....

...........do..........

...... . ....do. ....... ..

n

3 

149

30 

32

16 

35

184 

26 

65 

30 

29

Cadmium in ash (ppm)

AM

0.5 

15

2.6 

1.6

24 

15

3.9 

8.4 

4.3 

11 

3.3

GM

0.5 

12

2.3 

1.4

19 

14

3.2 

6.2 

4.0 

9.0

2.7

GD

2.05

1.57 

1.47

1.96 

1.48

1.90 

2.17 

1.43 

1.97

1.84
G8 CONTRIBUTIONS TO GEOCHEMISTRY

the analytical data given in this table were derived from the estimated geometric means and geometric deviations by using a technique developed by Sichel (1952) and described by Miesch (1967). 

The arithmetic means in table 1, unlike the geometric means, are 

estimates of geochemical abundance (Miesch, 1967) and are directly comparable to arithmetic means commonly employed in 

presentations of geochemical averages in the literature. Arithmetic means are always larger than corresponding geometric 

means (Miesch, 1967, p. Bl) and are estimates of the fractional 

part of the population that consists of the element of concern 

rather than of the typical concentration of the element in a population of samples.

The data in table 1 indicate that the cadmium contents of these 

plants that grew in environments low in cadmium are determined 

largely by the abilities of the different species to absorb cadmium, 

for there seem to be greater differences in cadmium concentration 

among species than probably exist among the soils in which the 

plants were rooted. For example, samples of shagbark hickory 

contained an average of 5 times as much cadmium as was found 

in white oak, yet both species were collected in pairs from the 

same soils and, presumably, were exposed to the same quantities 

of environmental cadmium.

ENVIRONMENTS THAT HAVE UNCOMMONLY HIGH LEVELS OF CADMIUM

NATURALLY OCCURRING CADMIUM CONCENTRATIONS

For those plants growing in soils that contain more than certain background amounts (as yet not defined) of cadmium, the 

cadmium content of the plant tissues tends to increase with increasing soil concentrations, at least in some environments. 

Lounamaa (1956), in his studies of trace elements in plants growing wild on different rocks in Finland, reported that the cadmium 

content of bryophytes (mosses) ranged from 1 ppm in ash of 

samples from nonmineralized rock to 100 ppm in ash of two samples from sphalerite-enriched substrates.

Certain peat bogs in Orleans County, N.Y., are enriched in zinc, 

lead, and cadmium by the entrance of ground water from dolomite beds that contain concentrations of these elements (Cannon, 

1955). Thirty years after many of these bogs had been drained, 

Cannon (1970) reported the cadmium concentrations in certain 

vegetables and native plants that grew on the soils of the drained 

bogs as follows: Carrots (Daucus carota L.), roots washed and 

peeled, 8 ppm in ash, or 0.36 in dry material; potatoes (Solatium 

tuberosum L.), 7 ppm in ash, or 0.36 ppm in dry material; 15 

vegetable samples, median 0.12 ppm in dry material, range 0.05 

to 0.96; and seven samples of native vegetation, median 0.18 ppm
CADMIUM IN PLANTS G9

in dry material, range less than 0.09 to 0.67 ppm. These median 

cadmium concentrations, however, are lower than the concentrations reported by Bowen (1967a, b) for his "standard kale" 

sample.

In a U.S. Geological Survey study of trace elements in plants 

as applied to prospecting for mineral deposits in the Rocky Mountains, several species of trees and shrubs were sampled and analyzed for cadmium and other elements (G. C. Curtin and H. D. 

King, written commun., 1971). The areas sampled were either 

mining areas or areas that might contain undiscovered mineral 

deposits, as indicated by anomalous levels of some metals in the 

soils for example, cadmium in the soil humus ranged from less 

than 1 to 10 ppm. Ash of leaves and stems (branches) were analyzed separately for cadmium by a modified semiquantitative 

spectrographic method that results in a lower detection limit of 

1 ppm in plant ash (Hosier, 1972). Mean cadmium concentrations 

found in these samples are given in table 2.

Data in table 2 show that the stem ash generally contains about 

twice as much cadmium as leaf ash. This difference in concentration indicates that the cadmium in the samples was largely taken 

up from soil by the roots and was transported to stems and leaves, 

rather than having been directly accumulated by the plants from 

atmospheric fallout. Because of their relative configurations, stems 

have a much lower surface-to-volume ratio than leaves; therefore, 

if the source of cadmium had been airborne particles, stems would 

be expected to contain the lesser amount of cadmium. Moreover, 

the fact that the area where the samples were collected was far 

removed from significant industrial or vehicular pollution suggests 

that airborne cadmium would account for only a very small part 

of the total cadmium in the plant tissues.

The cadmium contents given in table 2 suggest that species of 

trees differ greatly in their ability to concentrate cadmium in their 

tissues. For example, in analyses of coniferous trees, ash of limber 

pine leaves and stems contained an average of 3.4 and 5.5 ppm 

cadmium, respectively, whereas lodgepole pine contained 10.5 ppm 

cadmium in leaves and 16.6 ppm in stems. Contrasts among deciduous trees are provided by mountain maple, whose leaves contained 1.6 ppm cadmium and whose stems contained 4.9 ppm, and 

willow, whose leaves and stems contained 15.7 and 37.6 ppm, respectively. However, without information on the abundance of 

cadmium in the environments where these different species grew, 

differences in average cadmium content in tissues among species 

cannot be attributed with certainty to differences in the inherent 

ability of species to accumulate cadmium. The usefulness of the 

species listed in table 2 as indicators of anomalous cadmium con-
G10 CONTRIBUTIONS TO GEOCHEMISTRY

TABLE 2. Mean cadmium concentrations and ash yields in

[n, number of samples ; GM, geometric mean ; GD,

Leaves

Common and scientific name

Colorado blue spruce (Picea puns/ens

Douglas-fir (Pseudotsuga menziesii (Mirb. )

Engelman's spruce (Picea engelmannii

Juniper (Juniperus communis ssp. nana

Kinnikinnik (Arctostaphylos uva-ursi (L.)

Lodgepole pine (Pinus contorta var.

Mountain maple (Acer glabrum Torr.).. .......

Ponderosa pine (Pinus ponderosa var.

Snowberry (Symphoricarpus occidentalis 

Hook.).......... ......... . ....

Sticky laurel (Ceanothus velutinus Dougl. )........ 

Quaking aspen (Populus tremuloides Michx.).... 

Wild gooseberry (Ribes sp )

Willow (Salix sp.). ...

Cadmium in ash (ppm) Percent ash

n

1 

15 

5 

14

1 

6

24 

5

12

1 

1 

22 

2 

4

GM

2.0 

1.1 

2.5

5.0 

3.4

10.5 

1.6

5.7

2.0 

<2.0

7.7 

1.2 

15.7

GD

1.77 

1.36 

2.17

2^30

1.36 

3.06

1.45

1.60 

1.72

GM

3.3 

3.6 

4.9 

4.4

4.1 

2.8

2.0 

5.3

2.0

5.8 

4.4 

5.9 

5.9 

6.2

GD

1.28 

1.30 

1.16

L22

1.25 

1.12

1.27

1.16 

1.13

centrations in soils cannot be evaluated without data on the same 

species in environments similar in all characteristics except the 

cadmium levels in the soils.

A possibly valid comparison of cadmium concentrations in ash 

of uncultivated plants growing in mineralized areas with those of 

plants from areas that have only background levels of cadmium 

is provided by juniper from mineralized areas of Colorado (table 

2) that had an average cadmium content of 5.5 ppm in stems and 

2.5 ppm in leaves, and red cedar from areas of presumably normal 

cadmium levels in Missouri that had an average cadmium content 

of 1.6 ppm in composite samples of stems and leaves. However, 

these differences in average cadmium concentration may only reflect species differences in ability to absorb cadmium. If the cadmium content (1.6 ppm) of Missouri red cedar samples from areas 

of normal cadmium is compared with the cadmium content 

(9.3 ppm) of Missouri roadside samples of the same species that 

had been contaminated by lead ore (Connor, Shacklette, and Erdman, 1971), the ability of this species to respond to different 

environmental levels of cadmium is apparent.

CADMIUM FROM VEHICULAR, INDUSTRIAL. AND URBAN POLLUTION

The cadmium concentration in mosses (principally Hypnum 

citpressiforme L.) has been used as an index to airborne cadmium 

pollution in Sweden. The normal cadmium content of this moss 

was reported to range from 0.7 to 1.2 ppm on a dry-weight basis. 

In the center of the Greater Stockholm area, this plant contained 

as much as 7.5 ppm cadmium (Riihling, 1971, p. 2) and in the cen-
CADMIUM IN PLANTS Gil

tree and shrub samples from mineralized areas in Colorado

geometric deviation ; ......... no data available]

Plant part

Leaves Con. Stems (branches)

eome ric ean vPP ' Cadmium in ash (ppm) Percent ash Lreometric mean ippm)

to units of dry 

weight (ppm)

0.07

.05

.11

.21 

.10

.21 

.09

.11

.12

'^45 

.07 

.97

n

1

15

5

14

1 

6

24 

5

12

1 

1 

22 

2 

4

GM

2.0

7.3

6.4

5.5

7.0 

5.5

16.6 

4.9

9.8

5.0 

1.0 

13.7 

1.7 

37.6

GD

2.47

1.56

1.66

2.30

1.54 

2.00

1.63

IA5 

2.19

GM

1.5

2.7

3.5

4.7

3.3 

2.5

2.3 

3.5

2.2

1.8 

3.0 

5.6 

4.7 

4.0

GD

1.36

1.25

1.13

1.15

1.12 

1.26

1.42

l"21 

1.31

to units of dry 

weight (ppm)

0.03

.20

.22

.26

.23 

.14

.38 

.17

.22

.09 

.03 

.77 

.08 

1.50

ter of Oskarshamn, 81.7 ppm (Riihling, 1969, p. 2). Oskarshamn, 

a city of about 25,000 population, has two important centers of 

heavy-metal emissions a sulfuric acid plant that emits copper, 

cobalt, and zinc, and a storage-battery factory that releases cadmium, chromium, nickel, and lead into the atmosphere (Ake 

Riihling, written commun., 1969).

Mosses and their underlying soils were sampled by the author 

at 10 pairs of sites along highways in south-central Missouri. One 

site of each pair was 15-20 feet from the highway pavement; the 

other, 100-600 feet from the highway. All soil samples contained 

less than 1 ppm cadmium. The difference in average cadmium 

concentrations of the paired moss samples was not significant: 

cadmium in ash of samples from sites near the road averaged 

5.6 ppm (range, 2.2-22.0 ppm), and in samples more distant from 

the road, 5.2 ppm (range, 1.8-12.0). The moss species sampled 

were Anomodon rostratus (Hedw.) Schimp., Atrichum angustifolium (Brid.) B.S.G., Cirriphyllum illecebrum (Hedw.) L. Koch, 

Dicranum scoparium Hedw., Hedwigia ciliata (Hedw.) P. Beauv., 

Leucobryum glaucum (Hedw.) Angstr. ex Fr., Mnium affine 

Bland, ex Funck, and Polytrichum commune Hedw. The dust contamination of some samples, which could not be removed completely by washing, may have obscured the difference in cadmium 

content, if present, between the two lots of samples.

The effect of roadside contamination by motor vehicles on the 

cadmium content of grass was reported by Lagerwerff and Specht 

(1971) to diminish with distance from the road; dry grass samples 8 m (meters) from the road contained 0.63-1.25 ppm cad-
G12 CONTRIBUTIONS TO GEOCHEMISTRY

mium, whereas those 32 m from the road contained 0.25-0.58 ppm. 

These authors attributed the cadmium in the grass samples to both 

soil and aerial sources.

In a U.S. Geological Survey study of element concentrations in 

sampling media on roadsides in Missouri, Connor, Erdman, Sims, 

and Ebens (1971) found no significant difference between the 

cadmium content in roadside cedar trees (Juniperus virginiaua 

L.) exposed to presumably normal amounts of cadmium from vehicular traffic and that in trees growing at sites more distant 

from the roads. Connor, Shacklette, and Erdman (1971) reported 

that cedar-tree samples from a roadside in Missouri that was 

believed to be contaminated with lead ore blowing from passing 

ore trucks had an average cadmium content of 9.3 ppm in the ash 

of leaves and branches. Similar samples from trees that grew at 

the same site but at greater distances from the road averaged 2.8 

ppm cadmium. A sample of a pine (Pinus echinata Mill.) that 

grew with the cedars at this contaminated site contained 20 ppm 

cadmium in the ash of its leaves and branches. Cadmium concentrations in samples of surface soils at this site were all less than 

1 ppm.

Studies of environmental pollution resulting from industrial 

smelting of ores in the Helena Valley area of Montana were conducted by the U.S. Environmental Protection Agency. Samples of 

soil from the plow zone and deeper zones were collected and analyzed for cadmium, lead, zinc, and arsenic by Miesch and Huffman 

(1972). Concentrations of cadmium were found to be greatest in 

samples of the upper soil layers from sites on the downwind side of 

the smelter stack; cadmium in these samples ranged from 26 ppm 

at a distance of 1 mile from the stack to 2 ppm at a distance 

of 8 miles. Hindawi and Neely (1972) reported the cadmium concentration in vegetation (alfalfa, lettuce, pinto bean, beet, and 

carrot) to range from 0.1 ppm when grown in vermiculite to 

8.6 ppm when grown in garden soil near the smelters (whether dry 

weight, ash weight, or wet weight was used in calculating concentrations was not stated). Samples of a variety of garden plants 

and field plants obtained from gardens and ranches in the area 

ranged in average cadmium concentration from less than 0.05 to 

9.8 ppm, on a wet-weight basis. Dry-weight or ash-weight conversions were not given for these data; therefore, they cannot be 

compared with other data (except those of Schroeder and Balassa, 

1963) in this report. Cadmium content in soils used for the 

greenhouse and garden experiments conducted by Hindawi and 

Neely ranged from 2.0 to 56 ppm. Results of their greenhouse 

experiments led them to conclude that plants can absorb cadmium 

through their roots.
CADMIUM IN PLANTS G13

Gordon (1972) reported that cadmium concentrations in samples from the Helena Valley area, Montana, ranged from 1 to 

6 ppm in grasses and from 6 to 33 ppm in soils (both ranges determined on a dry-weight basis). He also reported that cadmium 

concentrations in garden soils ranged from less than 1 to 31 ppm, 

and in lettuce that grew on these soils, from less than 1 to 28 ppm 

(dry-weight basis). Cadmium concentrations in samples of lettuce 

from Missoula, Mont, (where there was no smelter pollution), 

were reported to be less than 1-1.2 ppm, and in samples of garden 

soils less than 1 ppm.

Warren, Delavault, and Fletcher (1971) suggested that the 

background concentration of cadmium in soils is 0.5 ppm (the 

same value as that given as average by Vinogradov, 1959). These 

investigators (1971, p. 5) listed cadmium concentrations that they 

considered "normal or average" in ash of some vegetables as follows: Lettuce, potato, cabbage, and beet, 1 ppm; bean (except 

broad bean), 2 ppm. They reported maximum cadmium concentrations in ash of the same kinds of vegetables collected from 

industrial and urban communities in Canada and the United Kingdom as follows: Lettuce, 87 ppm; potato, 12.7 ppm; cabbage, 

3.9 ppm; bean, 2.4 ppm, and beet, 3.0 ppm.

Certain areas in Japan have been heavily polluted with cadmium 

and other metals released by mines and smelters, and chronic 

poisoning of the population has occurred. This pollution, which 

was extensively investigated by Kobayashi (1972, p. 123-124), 

was of two types: (1) that originating from waste water from 

mines and smelters, and (2) that emanating from smelter chimneys. At some locations both airborne and water-borne cadmium 

were present. The water-borne cadmium entered irrigation systems and was carried to the soil in rice fields, where it was absorbed by rice plants. The polished rice grains in 27 samples from 

fields polluted by both water-borne and airborne cadmium had an 

average cadmium content of 0.49 ppm; the cadmium content of 

wheat and barley was several times greater than that of rice.

Studies of the annual growth rings of sugi trees (Cryptomeria 

japonica Don) that grew in the Jinzu River basin of Japan where 

cadmium pollution derived from mining and smelting is widespread were reported by Ishizaki, Fukushima, Kurachi, Sakamoto, 

and Hayashi (1970). They found that the narrow growth rings 

indicated suppression of the trees from 1910 to 1943 and attributed this suppression to the absorption of cadmium that was released from smelter clinkers through the action of sulfur dioxide. 

High cadmium values were found in the tree rings formed during 

this period.
G14 CONTRIBUTIONS TO GEOCHEMISTRY

In studies of contamination from a zinc refinery, Kobayashi 

(1972) found that the concentration of cadmium in mulberry 

leaves (used for silkworm feed) was inversely proportional to the 

distance of the mulberry trees from the refinery. At 400 m, the 

dried leaves contained about 17 ppm cadmium; at 1,000 m, 

7 ppm; and at 2,500 m, 4 ppm. Control samples of the leaves 

contained less than 1 ppm. Approximate cadmium concentrations, 

in parts per million, in dried vegetables from gardens at various 

distances from the refinery were reported as follows: Asparagus, 

8; azuki beans, 1; burdock root, 5; cabbage outer leaves, 6; cabbage inner leaves, 3; carrots, 8; Chinese cabbage, 41; corn, 2; 

eggplant fruit, 8; greens, damaged, 56; greens used for salting, 

32; potatoes, 2; pumpkin, <1; radish roots, 3; radish leaves, 15; 

taro potatoes, 2; turnip roots, 5; turnip leaves, 15; tomatoes, 2; 

and Welsh onions [leeks?], 14. An unidentified species of moss 

that grew in the gardens contained 61 ppm cadmium, the highest 

cadmium content found in any plant sample. In both the areas 

studied, Kobayashi (1972, p. 125) reported that "the principal 

cause of the high content of trace metals in plant tissues was the 

absorption and accumulation of metals through the roots from the 

polluted soil, rather than direct deposition of metals on the plant 

surfaces from the metal-containing air."

This observation by Kobayashi without further explanation 

regarding the manner in which cadmium entered the plants does 

not seem to be supported by the levels of cadmium that he gave 

for vegetables, although it may be true for the cadmium contents 

that he reported for rice, wheat, and barley. The vegetable analyses show relatively low amounts of cadmium in plant parts that 

have a low surface-to-volume ratio (asparagus stems, pumpkin, 

tomato, and eggplant fruit), in parts that are surrounded by protective outer structures (bean and corn seeds), and in plant parts 

that grow underground (potatoes, radish roots, taro potatoes, and 

turnip roots). Leaves, in contrast, have a high surface-to-volume 

ratio and were shown to usually contain much larger amounts of 

cadmium. The highest concentration of cadmium was found in a 

moss sample. Because of the finely divided nature of moss plants, 

they have an extremely high surface-to-volume ratio, and their 

cadmium contents are expected, therefore, to be strongly affected 

by airborne cadmium pollution.

A species of fruticose lichen (Cladonia alpestris (L.) Rabenh.) 

was sampled as an indicator of cadmium pollution from a recently 

constructed zinc refinery in Finland (Jaakkola and others, 1971). 

Background cadmium concentrations in this species, determined 

by analyzing specimens from Lappland, were found to be 0.1-
CADMIUM IN PLANTS G15

0.2 ppm in dry plants. Samples from locations near the zinc refinery 

contained about 1 ppm cadmium, and those collected elsewhere in 

Finland contained 0.3-0.4 ppm. Jaakkola, Takahashi, and Miettinen stated (p. 7) that in this lichen "Only 6 months of operation 

have increased the cadmium level five-fold at about 1 kilometer's 

distance from the zinc works, but no increase is yet noticeable at 

a distance of about 4 kilometers."

A fruticose lichen (Cladonia trangiferina) that grew on shallow soil over dolomite was sampled by the author near Bellevue, 

Iron County, Mo., in an area apparently free from airborne pollution. Ash of this sample, No. D414121, contained 1.8 ppm cadmium (C. S. E. Papp, analyst), which is equivalent to about 

0.19 ppm in dry material, a value that agrees well with the cadmium background value for the Lappland lichens.

Cowgill (1970) reported a study of the hydrogeochemistry of 

a small lake in Connecticut that was subjected to pollution resulting from the development of the lake basin as a residential area. 

The pollution arose from raw sewage emptied into the lake and 

from vehicular emissions. She found (p. 58) an average content 

of 17 ppm cadmium in the dry matter of duckweed (Lemna minor 

L.), a very small floating aquatic plant. The source of cadmium 

was believed to be snow and ice in the drainage basin of the lake, 

because the increase in cadmium of the lake water occurred during 

periods of snowmelt. Catkins of willow (Salix nigra L.) and blossoms of apple (Pyrus mains L.) that grew on the lake shore contained 25 ppm and 24 ppm cadmium, respectively, in dry material. 

Cowgill implied that vehicular emissions had contaminated these 

plants with heavy metals. These cadmium values for plants seem 

to be abnormally high, as judged from the degree of pollution 

that was thought to be present. In regard to preparation of the 

plant samples for analysis, she stated (p. 16) : "Two and a half 

grams [of pulverized dry material] were placed in a cadmium ring 

and pressed at 1.6 metric tons cm~V In using this procedure, significant contamination of the sample by the cadmium ring seems 

highly probable.

Results of a study of airborne nonferrous metal pollution in the 

area around Swansea, Wales, as measured by analyses of soil, a 

moss (Hypnum cupressiforme), and a grass (Festus rubra), were 

reported by Goodman and Roberts (1971). These authors found 

these sampling media to be useful indicators and integrators of 

aerial metallic burdens. In areas of little suspected aerial pollution 

the moss contained 1.0-1.8 ppm cadmium in dry matter, the grass 

contained 0.7-0.8 ppm, and the soil contained 0.4-0.5 ppm. In 

heavily contaminated areas, the following cadmium concentrations
G16 CONTRIBUTIONS TO GEOCHEMISTRY

were found: Moss, 1.0-9.5 ppm (the moss could not grow at the 

sites of greatest contamination) ; grass, 1.3-40.0 ppm; and soil, 

0.5-26.0 ppm. They reported that grass which caused the death 

of a horse by plumbism contained 9.9 ppm cadmium, whereas 

samples of the control grass contained 1 ppm. In transplant experiments, specimens of the moss in nylon mesh bags were suspended from trees at sites having various levels of airborne metal 

pollution. At the site of greatest pollution, the cadmium level in 

the moss specimens rose from 2.0 ppm (background value for this 

moss) to 337 ppm in the dry matter after 2 weeks' exposure. In 

evaluating their technique as useful indicators of airborne metal 

pollution they stated: "Our methods are much more rapid, inexpensive, and probably more meaningful than spot-sampling of 

air by nitration for which prohibitive resources are needed for a 

few months' operation."

Tyler (1972) discussed the effects on plants and soils of heavymetal concentrations that originated from local industrial pollution in an area of central Sweden. He reported the following 

cadmium values (mg kg in dry material) in different plants and 

plant parts:

Spruce (Picea abies) samples: First-year twigs, 5.4; secondyear twigs, 4.6; third-year twigs, 4.2; fourth-year twigs, 

3.3; 5- to 7-year twigs, 2.7; bark, 2.5; roots, 1.5; fine 

roots, 2.7.

Mosses: 30.

Bilberry (Vaccinium myrtillus) shoots: 4.4.

Hairgrass leaves: 7.6.

This heavy-metal pollution was postulated by Tyler (1972) to 

reduce productivity of the ecosystem through a chain of events 

that begins with a reduced rate of decomposition of the forest 

litter owing to the adverse effects of these metals on soil microorganisms. This reduced decomposition leads at first to an increase 

in the amount of surficial litter, but because the essential plant 

nutrients held in the undecomposed litter are not available for 

recycling through the ecosystem, primary productivity by photosynthetic plants is gradually reduced. The reduced production of 

litter results in the distribution of the continuing heavy-metal 

fallout through a smaller amount of organic matter in the substrate ; therefore, the amount of heavy metals per unit of substrate 

material is increased. These increased accumulative concentrations 

were thought to cause a rapid decrease in productivity of the ecosystem.

AIRBORNE CADMIUM MEASURED BY ANALYSIS OF SPANISH MOSS

In a U.S. Geological Survey study of elements in Spanish moss 

(Tillandsia usneoides L.), samples were obtained from 123 sites
CADMIUM IN PLANTS G17

throughout the range of the plant and were analyzed for 37 chemical elements. This flowering plant is in the Bromeliaceae (pineapple) family and is not a true moss (bryophyte), although 

superficially it resembles some mosses. It grows commonly on the 

branches of trees, but also at places on other supports such as 

posts, fences, and utility wires, in the Atlantic and Gulf coastal 

plains. Its range in the United States extends from Great Dismal 

Swamp in North Carolina to southern coastal Texas; inland it 

ranges as much as 250 miles from the coast, in southwestern 

Arkansas (fig. 1). The complex factors thought to control the distribution of this plant were discussed by Garth (1964).

Although short-lived structures resembling roots support young 

seedlings, mature Spanish moss plants have no root system and 

are supported on trees and other objects by means of their intricately branched stems and interwoven leaves that collect all the 

essential nutrients, and other materials, from the atmosphere. 

These nutrients are gasses, materials carried in particulate matter 

(dust), and solutes in airborne water; consequently, the plant has 

no direct dependence on local soil for its nutrients. In addition to 

the finely divided plant body, abundant peltate scales throughout 

the plant present a very large surface area in relation to the volume of the plant, thus providing an effective filter for airborne 

materials and a ready absorbent for \vater. In some habitats Spanish moss may receive drip water that contains nutritive materials 

in the leachate from tree leaves, but the plant grows well without 

this added source of nutrients.

The samples were analyzed in a sequence that was randomized 

with respect to geographic location and date of collection. The 

cadmium analyses \vere made by T. F. Harms, using an atomicabsorption method. The analytical determinations were transformed to logarithmic values through a computer program which 

also determined the minimum and maximum values, as well as the 

basic statistics, and printed a histogram of the analytical values 

and a table of frequencies and cumulative frequencies for each 

class designation on the histogram. Through examination of the 

table of frequencies, the range of reported values was divided into 

five classes of cadmium concentration that centered around the 

geometric mean, as shown on the histogram in figure 1. Symbols 

were selected to represent each class, and the appropriate symbol 

was placed on the base map at the collection locality of each sample (fig. 1). The same procedure was followed for presenting the 

ash contents of the samples (fig. 2).

The data presented in figure 1 suggest that, in general, the 

concentrations of cadmium in Spanish moss are related to the degree and kind of aerial pollution at a location. In order to present
G18 CONTRIBUTIONS TO GEOCHEMISTRY

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CADMIUM, IN PARTS PER MILLION

FIGURE 1. Localities of Spanish moss samples, and cadmium concentrations 

found in these samples. Seashore localities are plotted offshore. Geometric 

mean, 7.9; geometric deviation, 1.65; number of samples and analyses, 122.
CADMIUM IN PLANTS G19

the contrast in localities where the high-cadmium and the lowcadmium samples were collected, samples in the highest category 

(12.2 ppm and more) and the lowest category (5.3 ppm and less), 

as shown by the histogram in figure 1, are ranked within each 

category by cadmium content and are discussed below.

The samples having extremely high cadmium contents (at least 

20 ppm), arranged in decreasing values, are from Natchez, Adams 

County, Miss. (27 ppm) ; Limona, near Tampa, Hillsboro County, 

Fla. (25 ppm) ; Panama City, Bay County, Fla. (23 ppm) ; and 

East Baton Rouge Parish, La. (21 ppm). These locations are all 

in areas where considerable industrial and vehicular contamination of the air is expected to occur.

Samples having very high cadmium contents (15-19 ppm) were 

collected at the following locations: Near Batchelor, Point Coupee 

Parish, La. (19 ppm) ; 8 miles east of Roper, Washington County, 

N.C. (19 ppm) ; near Verona, Onslow County, N.C. (17 ppm) ; 

6 miles west of Yazoo, Yazoo County, Miss. (16 ppm) ; Sugar 

Land, Fort Bend County, Tex. (15 ppm) ; and near Monticello, 

Jefferson County, Fla. (15 ppm).

Samples having high cadmium concentrations (12.2-14 ppm) 

were collected at the following locations: Near Latta, Dillon 

County, S.C. (14 ppm) ; near Lake City, Florence County, S.C. 

(14 ppm) ; 5 miles east of the junction of Interstate Highway 10 

with 1-160, Harris County, Tex. (14 ppm) ; 2 miles south of Jackson, Hinds County, Miss. (13 ppm) ; Beaumont, Jefferson County, 

Tex. (13 ppm) ; 2 miles north of Valdosta, Lowndes County, Ga. 

(13 ppm) ; Charleston, Charleston County, S.C. (13 ppm) ; and 

about 3 miles west of Stillmore, Emanuel County, Ga. (13 ppm).

At some of the locations listed for the above two categories of 

cadmium values, potential sources of aerial pollution were evident, 

whereas at others, none was noted but still might have been 

present.

Locations of samples plotted in figure 1 that fall in the lowest 

category of cadmium values (2.0-5.3 ppm), as illustrated by the 

histogram, for the most part were expected to have minimal airborne cadmium pollution. Within this category, samples with a 

cadmium content of 2 ppm were considered to be extremely low 

in cadmium concentration. One of these samples was from an area 

where significant airborne cadmium pollution is extremely unlikely Paradise Key, Everglades National Park, Bade County, 

Fla. Another sample that contained 2 ppm cadmium was taken 6 

miles south of Monticello, Lawrence County, Miss., in a rural environment where airborne industrial pollution is expected to be
G20 CONTRIBUTIONS TO GEOCHEMISTRY

low, and the third sample in this category was from West Palm 

Beach, Palm Beach County, Fla.

Samples found to be very low in cadmium (2.2-3.8 ppm) were 

from the following locations: Vero Beach, Indian River County, 

Fla. (2.2 ppm) ; Fort Lauderdale, Broward County, Fla. (3 ppm) ; 

7 miles west of Opp, Covington County, Ala. (3.4 ppm) ; Robert, 

Tangipahoa Parish, La. (3.6 ppm) ; 1 mile northeast of Winnsboro, Franklin Parish, La. (3.6 ppm) ; and 1 mile east of San 

Jacinto, Polk County, Tex. (3.8 ppm).

Samples considered to be low in cadmium (4.2-5.2 ppm) were 

from the following locations: Route 8 at the Sabine River bridge, 

Vernon Parish, La. (4.2 ppm) ; Georgetown, Georgetown County, 

S.C. (4.2 ppm) ; Coximba area, Marco Island, Collier County, Fla. 

(4.3 ppm) ; 3 miles south of the Letohatchee exit from Interstate 

Highway 65, Lowndes County, Ala. (4.4 ppm) ; 1 mile east of the 

Neches River on Route 190, Jasper County, Tex. (4.6 ppm) ; Cross 

City, Dixie County, Fla. (4.8 ppm) ; Route 27 at the State line, 

Walthall County, Miss. (4.8 ppm) ; Gibson, Terrebonne Parish, 

La. (5 ppm) ; on the beach at Josephine, Baldwin County, Ala. 

(5.2 ppm) ; and Hunting Island State Park, Beauford County, 

S.C. (5.2 ppm).

The percentages of ash obtained by burning the dry samples are 

presented in figure 2. A comparison of ash contents of the samples 

(fig. 2) and their cadmium concentrations (fig. 1) shows no consistent relationship between the two factors. Some samples that 

are placed in the highest category of cadmium concentrations 

have high ash contents, whereas others have low ash contents. 

The samples classed as extremely low in cadmium all have high 

ash contents; other samples \vith low cadmium concentrations 

have low ash contents. These inconsistencies in the relation of 

cadmium and ash contents indicate that the surficial deposits on 

Spanish moss are not necessarily similar in composition from place 

to place and that both composition and amount of the deposits influence the cadmium concentrations in ash of the plants.

Only a small proportion of the dry Spanish moss tissue is believed to consist of noncombustible material (ash) probably no 

more than 2 percent. Ash percentages greater than this most likely 

represent surficial accumulations (principally dust) that are not 

held within the tissues. If these deposits are largely composed of 

dust from soil, increasing the amount of dust most likely will depress the proportion of cadmium, because soil typically contains 

very little cadmium. The effect of this type of deposit on the concentration of cadmium in ash is illustrated by a sample from the
CADMIUM IN PLANTS G21

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FIGURE 2. Localities of Spanish moss samples, and ash content of the samples. Seashore localities are plotted offshore. Geometric mean, 4.5; geometric deviation, 1.40; number of samples and analyses, 122.
G22 CONTRIBUTIONS TO GEOCHEMISTRY

bank of the San Antonio River, Kearns County, Tex., that was 

very heavily contaminated with soil dust (34 percent ash) and 

contained the lowest concentration of cadmium (0.8 ppm) that 

was found in this study. This highly anomalous sample was excluded from the data presented in figures 1 and 2.

On the other hand, if the surficial accumulations consist largely 

of particulate matter resulting from the combustion of coal and 

petroleum products, or from certain types of industrial processes, 

an increase in amount of these surficial deposits most likely will 

increase the cadmium content of the plant ash, yet the ash yield 

may be low. The four highest concentrations of cadmium found 

(27, 25, 23, and 21 ppm) were in samples that contained 4, 3.4, 5, 

and 2.8 percent ash, respectively. The cadmium in these samples 

is presumed to have come from industrial or vehicular airborne 

pollution. A study of the relative concentrations of many elements 

in the samples would give a better estimation of the type of airborne contamination that was present at each sampling location.

If the different kinds of particulate matter, as well as specific 

chemical elements, are considered to constitute atmospheric pollution, then the ash yield and element content of Spanish moss can 

be considered to be indicators of the relative degrees of total airborne pollution that has prevailed at locations over a period of 

several years.

DISCUSSION AND SUMMARY

Reliable estimates of typical cadmium concentrations in plant 

tissues are difficult to make because of the great variability in 

cadmium content among the different plant species and plant organs. Moreover, reports in the literature use different bases for 

computing cadmium concentrations in plants. For example, 

Malyuga (1964, p. 15) gave the cadmium concentration in plant 

ash but did not give the percentage of ash obtained from the dry 

tissue; Schroeder and Balassa (1963) gave cadmium values based 

on the wet weight of vegetables but gave neither the percentage 

of water nor the percentage of ash in the samples, and Hanna and 

Grant (1962), among many others, gave cadmium concentrations 

on a dry-weight basis but did not give the ash yield of the samples. 

Data on cadmium in plants that are presented for the first time 

in this report include cadmium concentrations in both ash and dry 

tissue, or give the concentrations in ash and the ash yield of the 

dry material with an equation that can be used to determine approximate cadmium concentrations in the dry tissue.

Another source of inconsistency in the reported data on cadmium in plants is the difference in methods of analysis that were 

used to obtain the data. Methods that were used included acid
CADMIUM IN PLANTS G23

digestion and atomic absorption, acid digestion and polarography, 

X-ray emission, neutron activation, and ashing by heat followed 

by emission spectrographic analysis of the ash. Some reports do 

not specify the analytical method that was used. This report does 

not attempt to judge the relative accuracy and precision of analyses determined by these different analytical methods.

To summarize data from the numerous reports of cadmium in 

plants, a table has been prepared that gives estimates of cadmium 

concentrations in plants or plant parts from environments presumed to have the normal low levels of cadmium, and in those 

from environments reported to have greater than normal levels 

of cadmium (table 3). Because most reports give cadmium on a 

dry-weight basis but do not give ash weights, the data from other 

reports were converted to parts per million in dry plant material. 

Some data based on ash weight, but without the ash yield being 

given, were converted to approximate concentrations in dry weight 

by assuming a reasonable ash yield for the particular kind of plant 

tissue that was analyzed. In instances of conflicting data, personal 

judgment was used in selecting the data to include in the table.

The values given in table 3 must be used with caution in evaluating specific problems of cadmium content in plants. The categories of plants and plant parts used in this table were, of 

necessity, often very broad and doubtless included certain species 

or varieties and plant parts whose normal cadmium contents differ 

greatly from the value given for the category. It should be noted 

that some of the cadmium values in the table were based on very 

few samples. Furthermore, for some kinds of plant materials, the 

cadmium concentrations in the environments where the plants 

grew were only loosely characterized, or were unknown.

Concentrations of cadmium in Spanish moss can be used to 

give estimates of the relative amounts of airborne cadmium at 

different localities within the regions where this plant occurs. 

Samples that contained the highest concentrations of cadmium 

were from locations where greater than normal levels of cadmium 

in the air were expected to occur as a result of industrial, domestic, and vehicular emissions. In contrast, samples that contained 

the lowest concentrations were from locations apparently remote 

from sources of significant cadmium pollution. Samples having 

cadmium concentrations in the central range of values could not 

be adequately evaluated without more detailed studies of the environments from which the samples came. f

The yield of ash obtained by burning Spanish moss plants provides an estimate of the relative total particulate contamination 

of the air at the different localities where the samples originated.
G24 CONTRIBUTIONS TO GEOCHEMISTRY

TABLE 3. Estimates of cadmium concentrations (parts per million in dry 

material) in some plants and plant parts

[........, no data available; <, less than the value stated]

Reported or estimated cadmium concentrations, 

or ranges in concentrations ______

Kind of plant or plant part

Marine algae... ..................... ........... ......... ......

Mosses (bryophytes) ........... ....... ..........

Lichens (fruticose type) ............ ............... ...

Grasses..--..------------.------.---..----------------------.

Alfalfa....... .....................................................

Grains :

Corn (Zea mays) .................................

Rice (polished) ......................................

Barley, wheat, and oats............. ..........

Vegetables :

Asparagus-. ............ ....... ...... .............

Beet root.. ...... ....... .............. ....... 

Cabbage leaves. ............................ .........

Carrots......... ....... ................... .......... ...

Chinese cabbage. ...................................

Eggplant fruit.......... ................. ............

Kale...... ..... ....... .......................................

Leafy vegetables used as pot herbs

or salads. .............. ...... ....................... .

Leeks...............-..--...--........ ......... .........

Lettuce....................................................

Potatoes....... .... ................................. ......

Spinach......... ..........................................

Turnip roots................ ........... .......... ...

Tomatoes...... ..........................................

Trees, deciduous :

Leaves-..------........................ ...... ............

Stems (branches) .................................

Trees, coniferous :

Leaves................................ ... . ... . ..

Stems.----.....-.....-....-...-..-.-.... .. . ... .....

Epiphytes (Spanish moss) ........... .........

Marine flowering plants (Zostera

marina) .... .....

In environments 

presumably having

normal cadmium

levels

0.1-1

0.7-1.2

0.1-0.4

0.03-0.3

0.02-0.2

0.1

0.1-0.5

.05

.05

<.35

1

0.3-0.5

0.3-0.5

0.05-0.3

0.6-1.2

0.1-2.4

0.1-1.3

0.1-0.9

0.1

0.23

In environments 

having greater than

normal cadmium

levels

8-340

1

0.6-40

10.2-2.4

2

0.5

-"0.1-1.5

8

0.24

6-12

8

41

8

3-50

14

4-16

0.6-2

5

15

2

4-17

0.14-1.5

0.05-1

0.03-1.5

1

17

1Original data given in wet weight; converted to concentration in dry material by assuming 

25 percent water in original sample.

2Original data given in wet weight; because the water content of grains is very low, these 

values were not converted to a dry weight basis.

Excessive contamination of the plants by participate soil materials 

reduces the reported cadmium values in the plant ash, whereas if 

the particulate material originated from combustion of hydrocarbons or from certain industrial processes, increased surficial contamination is thought to increase the reported cadmium values in 

the plant ash.

CONCLUSIONS

Cadmium in low concentrations most likely is a normal constituent of all plant tissues. The concentration in the tissue is determined by the inherent ability of a plant species to absorb cadmium
CADMIUM IN PLANTS G25

and by the cadmium concentration in the environment. At low 

levels of cadmium in soils, differences in cadmium content among 

plant species commonly are greater than differences in amounts 

of cadmium in the soils where the plants grew. Beyond certain 

background amounts of cadmium in soils, the cadmium content of 

plant tissue tends to increase with increased concentrations of 

cadmium in the soil.

Airborne cadmium, originating in emissions from the combustion of hydrocarbons or from certain industrial processes, may 

enter the soils and be absorbed by plants, or may be deposited on 

the surface of plants in particulate matter, until very high levels 

of cadmium are accumulated by the plant. There appears to be no 

natural means by which cadmium is eliminated from plant tissue, 

and no cultural practice has been found effective in reducing or 

preventing the absorption of cadmium by plants.

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U.S. GOVERNMENT PRINTING OFFICE: 1972 O 479-610