Arsenic Toxicity Studies— Clements and Munson 
169 
and 86 ppm of arsenic. Yet when these 
were grown in culture solution, only very 
much lower levels of trivalent arsenic were 
tolerated. The amounts of arsenic absorbed 
from the soil were more in line with the 
amounts of pentavalent arsenic absorbed 
from culture solution. It cannot be pre¬ 
sumed, however, that after arsenic is ab¬ 
sorbed in the pentavalent form, it remains 
as an inorganic compound after it becomes 
a part of the plant’s metabolism. 
The claim which has been made by many 
that arsenic at proper levels is stimulating to 
plant growth is not substantiated by the data 
presented here. Neither in water culture nor 
in soil culture is there any certain evidence 
of such stimulation. What slight gains from 
arsenic there may be are infinitesimal com¬ 
pared with the losses which are certain to 
come after the arsenic content passes critical 
levels. 
The arsenic which was added to the soil 
cans was not greatly reduced in amount 
either by the growth of the plants or by 
drainage which was provided. Even the 
large amounts of arsenic contained in the 
tomato plants grown in the high arsenic cans 
represent very small proportions of the total 
amount of arsenic in the soil. To calculate 
the time needed to extract the arsenic from 
the soil through continued use of tomato 
plants, assuming the highest extraction ob¬ 
served in these tests, would require some¬ 
thing over 100 crops. It is far better to stop 
the use of arsenic before critical levels are 
reached. It is apparent from this work, as 
well as from that of others, that no matter 
how large or how small the annual incre¬ 
ments to the soil may be, substantially all of 
the arsenic remains in the tilled layer. Re¬ 
ducing the increment of arsenic applied 
merely prolongs the time of grace. 
One observation needing to be brought 
into sharp focus is that, as shown in all fig¬ 
ures in the text, the point of sterilization for 
a given crop is very much higher than the 
point at which crop production begins to 
suffer curtailment because of accumulated 
arsenic. 
In red soil, Sudan grass began to suffer 
growth curtailment at about 115 ppm 
As 2 O s , the tomato at about 614 ppm, and the 
bean at about 314 ppm. From these respec¬ 
tive points on, the increasing curtailment 
varies for each crop. For the tomato the 
further drop is precipitous, less so for the 
bean, and still less so for Sudan grass. 
Sobering is the report from Queensland 
by Kerr (1939) that soil arsenic at the level 
of 600 ppm resulted in complete growth 
failure of sugar cane. In times of low prices 
for agricultural produce, even a 5 per cent 
curtailment of production due to soil arsenic 
may well mean the difference between profit¬ 
able and unprofitable operation. 
Studies carried on elsewhere have yielded 
some treatments which may be useful in cor¬ 
recting arsenic toxicity. The use of heavy 
phosphate applications, lime, iron oxide, and 
organic matter (perhaps filter cake) have 
shown promise of reducing the toxicity of 
arsenic excesses. None of these treatments 
reduces the arsenic content of the soil. 
Furthermore, most of these treatments are 
costly. Whether a single treatment is effec¬ 
tive for any length of time remains to be 
determined. 
There is only one permanent solution to 
the problem of arsenic accumulation so far 
as present-day information is concerned, and 
that is the cessation of arsenic applications. 
Substitution of other herbicides or other 
weed-control practices which at the moment 
may seem somewhat more costly may be the 
cheapest in the long run. Certainly there 
can be no reconciliation of a program of 
arsenic applications to the soil with any long- 
range view of agriculture. 
SUMMARY 
1. Studies made with plants treated with 
sodium arsenate and sodium arsenite in cul- 
