Pesticides residues
Tomatoes are prone to many pests (bacteria, fungi and insects). When tomatoes cultivated in conventional agriculture are treated with pesticides and herbicides, the amount of which may vary considerably from one country to another, depending on local regulations. Pesticides may remain at various levels in the plant. Prior to feeding animals on tomato crop residues, it is therefore important to know which treatment has been done, and when. This may be particularly important if they are fed to dairy animals because pesticides residues may go to the milk (Ibrahim et al., 2020; El-Sayed et al., 2012).
The amount of several pesticides residues could be reduced in tomato haulms by ensiling them with 3% molasses or with molasses + bacteria (Ibrahim et al., 2020). Ensiling with molasses decreased pesticide residues by 50% and 3% molasses + bacterial/fungal or yeast inoculum reduced them by 90% (Ibrahim et al., 2020). Drying may also be a valuable way to reduce pesticides in tomato haulms (El-Sayed et al., 2012).
Toxicity
There is no toxic substance detectable in the ripe tomato fruit, but green tomatoes contain high amount (1498 µg/g) of glycoalkaloids, 72% of which are still present in traditional fried green tomatoes from the southern US). Children who had made teas from leaves of tomato experienced severe reactions (Hardin, 1974). Tomato plants may contain variable amounts of a-tomatine, dehydrotomatine, toxic glycoalkaloids which are involved in the plant defense against virus, bacteria and insects. In a trial with rabbits, fresh tomato plants containing a-tomatine (1847µg/g in the leaves; 1547 µg/g in the stems), dehydrotomatine (304 µg/g in the leaves; 331 µg/g in the stems) and 20 mg/kg BW of solanine killed all animals within 24 hours (Barceloux, 2008; Patil et al., 1972). Senescent leaves contain up to 4.9 g/kg fresh weight of a-tomatin (Milner et al., 2011). However, a-tomatine, and dehydrotomatine were reported to be relatively less toxic than other glycoalkaloids (Milner et al., 2011).
Nitrate accumulation
Toxic levels of nitrates were found in dried tomato vines (Shlosberg et al., 1996).