This article throws light upon the eight main factors affecting toxicity. The factors are: 1. Taxonomic Differences 2. Stage of Growth 3. Condition of Plant 4. Soil and Cultivation 5. Climatic Conditions 6. Part of the Plant 7. Use of Nitrogenous Fertilizers and Weedicides 8. Host Factors.
Factor # 1. Taxonomic Differences:
Even slightest differences in plant may reveal unexpected differences in reference to hepato-toxic principles e.g. lantadene concentration is more in Lantaua Camara var aculeata (bearing red flowers) as compared to other taxa of same species.
Factor # 2. Stage of Growth:
Stage of growth is perhaps most important factor in determining the toxicity. Some species of sorghum when young and wilted or stunted contain fatal quantities of cyanides. Similarly, insecticidal principle, pyrethrin is present in enormous quantities in flower heads of Chrysanthemum cinerarifolium just before fertilization than at the stage nearing seed formation.
Though no generalization can be made, following parts of plants can attain maximum toxic/active principle at the stages given against each:
(a) Roots:
Roots, rhizomes and bark-during autumn or early spring.
(b) Leaves:
When photosynthetic reactions are at the peak i.e. at the time of the development of flowers.
(c) Flowers:
Just before pollination.
(d) Fruits:
The time nearing ripening period.
(e) Seed:
Attain maximum active principle when fully mature.
Factor # 3. Condition of Plant:
Some plants may become poisonous during sprouting or when wilted. Some plants may become poisonous when they are contaminated by fungi and fungi may liberate the toxic principles of plants.
Factor # 4. Soil and Cultivation:
The texture of soil, aeration of soil, amount of moisture in the soil and its temperature may greatly influence metabolic activity and hence the contents of toxic principles in plants. For example the nitrate contents of plants are greatly influenced by soil conditions.
Factor # 5. Climatic Conditions:
Climatic conditions such as temperature, humidity and nature and intensity of light also play an important role in the production of poisons due to their effect on metabolic activity. The alkaloidal contents are lower in rainy as compared to a dry spell.
Factor # 6. Part of the Plant:
The toxicity of roots, stems, leaves, flowers, fruits and seeds varies considerably even at the same stage of growth.
Factor # 7. Use of Nitrogenous Fertilizers and Weedicides:
Use of nitrogenous fertilizers and weedicides (e.g. 2, 4 D) increases the nitrate and cyanide contents of the plants.
Factor # 8. Host Factors:
The most important is rate at which plants are ingested and the time that the body takes to eliminate or destroy the poisonous principles.