Below is some useful information on conventional (non-organic) vegetable cultivation provided by an ex-farmer.
Vegetables are categorised into two groups: the leafy vege, and the beans/"qua". Leafy vege are the choy-sums, kailans, etc. "Qua" are the cucumbers, bitter gourds, brinjals, etc.
The chemical sprays used by most farmers are grouped into 2 categories: the fungicides and the pesticides. Fungicides are used to protect the plant from fungus, and pesticides are to ward off pests like bugs, caterpillars, snails, etc. The main culprits are the caterpillars.
For the leafy vege, normally less sprays are needed. When they are "young" they usually do not need any spray unless there is an outbreak of a fungus disease in the neighbourhood. But when the vegetable is maturing with many young leaves growing, farmers usually apply a round of pesticides to ward off the attack of pests. No fungicides are needed.
The label on the pesticide bottle says that it should not be used 1 week before harvest. Not all farmers follow that faithfull. How "toxic" a leafy vegetable is depends on the attitude of the farmer.
Beans/"qua" are "fruits" from a "plant", and these fruits are being harvested continously from the same plant which could last several months, not a one-time harvest as the leafy vege. In this case the farmers need to protect the "plant" as well as the "fruit". He has no choice but to spray the plants with both pesticides and fungicides.
Cucumber plant would have its first cucumber mature enough to be harvested 40 days after planting, and we can harvest cucumber (from a row of cucumber plants) every day for another 20 days. So what to do during this period of 20 days? The farmer just has to spray whatever pesticide/fungicide needed even if he is harvesting the fruits again the next day. During this harvesting period of 20 days he may spray 1 or 2 times of the needed chemicals since the spray is effective for a week only.
For long beans the harvest is on alternate days and the harvesting period is longer, up to 35 days. Chilli and brinjai plants can last even longer. So for this group of beans/"qua", the chances of eating one with recent toxic sprays is certainly very high. You might be eating one which was sprayed with pesticides the day before.