Which of the following is a symptom of poisoning from both organophosphates and carbamates?

The symptom of muscle tightness is indicative of poisoning from both organophosphates and carbamates, both of which act by inhibiting the enzyme acetylcholinesterase. This enzyme is crucial for breaking down acetylcholine in the neuromuscular junction, leading to excessive stimulation of the muscles. The resultant hyperactivity can manifest as muscle tightness, spasms, or cramping.

Organophosphates and carbamates share a similar mode of action, which is why symptoms can overlap. Muscle tightness particularly aligns with the neuromuscular effects of these substances as they disrupt normal muscle function and can lead to heightened muscle contractions.

In contrast, the other choices represent symptoms that may occur as well but are not exclusive or characteristic to the poisonings associated with organophosphates and carbamates. For example, nausea and vomiting can occur with a variety of toxins, increased thirst is not a classic symptom associated specifically with these pesticides, and dizziness and confusion are more general neurological symptoms that may arise from several chemical exposures or other conditions. Hence, muscle tightness stands out as a more specific symptom linked to the action of organophosphates and carbamates.