Arsenic Toxicity Studies— Clements and Munson 
157 
TABLE 3. BEAN 
Data for the accumulation of arsenic (as ppm 
AS2O3) AND PHOSPHORUS (AS PER CENT OF DRY 
WEIGHT), AS WELL AS DRY WEIGHTS OF PLANTS 
GROWN IN SOLUTIONS CONTAINING VARIOUS IN¬ 
CREMENTS OF PENTAVALENT ARSENIC (AS SODIUM 
ARSENATE) AT DIFFERENT PHOSPHATE LEVELS. 
ARSENIC 
IN 
SOLUTION 
DRY 
WEIGHT 
ARSENIC 
IN 
PLANT 
PHOS¬ 
PHORUS 
IN PLANT 
ppm AS 2 O 3 
gm. 
ppm AS 2 O 3 
% dry wt. 
Low phosphorus level (P = 10 ppm) 
0.00 
50 
trace 
0.64 
.1 
47 
2.5 
.55 
.25 
38 . 
2.8 
.51 
.5 
38 
2.5 
.50 
1.5 
28 
10.3 
.66 
2.0 
15 
13.7 
.58 
2.5 
11 
20.0 
.53 
Medium phosphorus level (P = 
60 ppm) 
0.0 
44 
trace 
.59 
.6 
48 
1.6 
.59 
1.5 
43 
2.7 
.60 
3 
35 
4.1 
.63 
6 
38 
5.1 
.66 
9 
26 
7.2 
.61 
High phosphorus level (P = 120 ppm) 
0.0 
57 
trace 
.63 
1.2 
54 
1.9 
.59 
3 
38 
2.7 
.66 
6 
37 
5.0 
.63 
12 
16 
38.0 
.72 
The Sudan grass plants growing in solu¬ 
tions containing 30 ppm and 60 ppm of 
pentavalent arsenic were apparently normal 
except for size, although they accumulated 
74.1 and 98.4 ppm of arsenic in their tops. 
Marked injury was noted at 90 ppm; the 
lethal concentration was between 90 ppm 
and 120 ppm. With trivalent arsenic, how¬ 
ever, a concentration as low as 3% ppm of 
arsenic in the culture solution resulted in 
cessation of growth, although the plant tops 
showed only 14.9 ppm of arsenic. The lethal 
concentration in the culture solution of the 
trivalent arsenic was between 11 ppm and 
15 ppm. Sudan grass can tolerate approx¬ 
imately 10 times as much pentavalent arsenic 
in the culture solution and in their tissues as 
trivalent arsenic. 
The bean plants were very intolerant of 
arsenic in any form. They grew quite nor¬ 
mally, however, in solutions containing 9 
ppm of pentavalent arsenic, from which 
they accumulated 7.2 ppm of arsenic in their 
tops. The lethal concentration was between 
12 ppm and 15 ppm of pentavalent arsenic. 
On the other hand, growth was prevented 
by a concentration of 2.25 ppm to 2.85 ppm 
of trivalent arsenic, despite an accumulation 
of only 4.9 ppm of arsenic in their tops. The 
lethal concentration of trivalent arsenic in 
the culture solution was between 2.85 ppm 
and 3.6 ppm. Trivalent arsenic is roughly 
four times as toxic to bean plants as is the 
pentavalent form. 
Comparisons made between the arsenate 
and arsenite series at the high and low phos¬ 
phorus levels show results similar to those 
discussed above for the intermediate phos¬ 
phorus level. 
The two forms of arsenic differ not only 
in lethal concentrations, but also in their 
immediate action on plant tissues. Triva¬ 
lent arsenic has a violent action, causing 
complete disintegration of the roots and 
burning of the tops in 1 or 2 days in lethal 
concentrations. Pentavalent arsenic, on the 
other hand, often takes several days to pro¬ 
duce any response other than wilting, even 
in concentrations that eventually prove 
lethal. 
Part II. The Effect of Different 
Phosphorus Levels on the Toxicity of 
Trivalent and Pentavalent Arsenic 
It was suggested by Hurd-Karrer (1939) 
that a relationship exists between arsenic 
toxicity and phosphorus availability. She 
used sodium arsenate in culture solutions at 
different phosphorus levels on studies with 
the oat plant and came to the conclusion that 
"in general, the arsenic was definitely toxic 
in the presence of less than four times as 
much phosphorus but non-toxic when there 
was more than four times as much.” 
Based on that observation, investigations 
were undertaken to compare the effect of 
