This method is an easy and sensitive tool for measuring of the total toxicity caused by chemical treatments as expressed by growth inhibition of the roots of onion bulbs. Results from Al-lium tests fit in well in a test battery composed of procaryotes and/or other eucaryotes (Fiskesjö, 1985a).
 

This method is applicable to the following types of samples:

1. natural waters (e.g., lakes, rivers, wells);
2. drinking water (e.g., tap water from different transport pipes;
3. domestic and industrial wastewaters, including sludge and leachates; and
4. water-soluble and-with solvents-water-insoluble chemicals. 

The most convenient is to use ordinary cold tap water as growth medium, for control and for the dilution of the test chemicals (Fiskesjö, 1985a). The tap water must be of good and known quality; with a pH around 7, with a Ca + Mg content of about 50-70 mg/L, and without any toxic ions (as, for instance, copper from copper pipes or aluminium in water froma private well with low pH). If copper pipes are used for the transport of drinking water, the copper may be avoided by running the water for some minutes before sampling it. (Health authorities in Sweden recommend a run of water for 3 min before sample is taken for analysis.)
 
According to the World Health Organization (1971), the "high-est desirable level" of Cu ions in drinking water for humans is 0.05 mg/L, and this is in agreement with results in the Allium test, since growth restrictions occur in Allium roots at Cu con-centrations higher than 0.05 mg/L (Fiskesjö, 1981, 1988).
 

When known concentrations are to be investigated, it is suitable to perform a preliminary test with 5 concentrations (and with a few onions in each) from 1.10-² M to 1. 10 -⁶ M, and thereafter increase the number of test concentrations within the interval showing growth restrictions..
 

• small sharp knife
• ruler

Onion bulbs of A. cepta are easily stored under dry conditions at + 10-20°C. Bulbs may be kept more than a year until mate-rial from the next season is available. However, some bulbs may dry up or be destroyed by mold, and the number of onions stored should be about 3 or 4 times the number needed for experiments.

Series of Bulbs in an ARium Test
 
In each test concentration, root length values from 10 onions in each series are used for calculations of a mean value for each test concentration. Some 20% of the onions, damaged by mold or from other reasons, may grow poorly. Therefore, 12 onions are started in each series, and the best 10 selected after 1-2 days cultivation-in the test samples as well as in the control. When only small amounts of samples are available, 5-6 onions are set up in each series.
 

TESTING PROCEDURE
 
With a minimum of work, this method will give results after 2-3 days. The unscaling of the bulbs, which is the most laborious part, will soon become a routine matter, as also the change of the test liquids every 24 h.
 

Arrange for each test concentration 12 test tubes in a test tube rack. Fill the test tubes with the test samples-12 tubes for each concentration.
 

Arrange for each test concentration 12 test tubes in a test tube rack. Fill the test tubes with the test samples-12 tubes for each concentration for a slight dry-up. Put one onion on top of each test tube, with the root primordia downward in the liquid.  
 

After 24 h, change the test samples, in the control and in all test concentrations, respectively. Repeat the change of liquids after 48 h (24 h + 24 h). With small amounts of test samples, only the evaporated amount may be replaced (0.5-1 mL).  
 

The degree of toxicity of the test chemicals or samples to the Allium roots is assessed by means of the root length values. A growth curve may be drawn based on the obtained values plotted as growth in percentage of control (ordinate) against test concentrations (abscissa). From the growth curve EC values are obtained: EC₅₀ = the effective concentrations where root growth amount to 50% of the controls (100%). The data are also suitable for statistical treatments.
 

A main point in this simple growth test method is that it may be performed by anybody without any specific training. The equipment is cheap and any type of test vessels may be used-for instance, in preliminary environmental studies. The results demonstrated as short or long root bundles are easy to interpret as environmental damage, as was the case when certain gardeners in southern Sweden in the late 1970s had their cultivations destroyed by wastewater outlets in the river whose water they used for the watering of vegetables. The same river water caused severe growth restrictions in AM= roots, when a series of onions were on this occasion first applied as a test 
system (FiskeqJ6, 1985b). 

Although a population, the onion sample will give a good mean of effects since a series of bulbs are used for each test sample.  
 

Fiskesjö, G. 1981. Allium test on copper in drinking water. Vatten 37:232-240.
Fiskeqjö, G. 1985a. The Allium. test as a standard in environmental monitoring. Hereditas 102:99-112.
Fiskesjö, G. Allium test on river water from Brafin and SaxAn before and after closure of a chemical factory. Ambio 14:99-103.
Fiskesjö, G. 1988. The allium test-An alternative in environmental studies: The relative toxicity of metal ions. Mutat. Res. 197:243-260.