As no reply, I tried to find internet link. One suggests:-

"...Although the effects of some neurotoxicants appear to be
reversible, at least in the short-term, chronic exposure may lead to
irreversible destruction of neurons and neural pathways...

Reversible (?) Neurotoxicity
Short-term low-level exposure to solvents, alcoholic beverages or
mood-altering drugs such as Valium and cocaine, neurotoxic pesticides
such as the organophosphate (OP) pesticides (Dursban and Diazinon are
familiar OP pesticides in the Houston area), and oxygen-depleting
chemicals such as carbon monoxide and methylene chloride generally
cause transient euphoria, sleepiness or other neurologic symptoms.
Whether or not there is subtle long-lasting but asymptomatic damage to
neurons or their pathways from low-level exposure is uncertain but
unlikely except in susceptible individuals.

Chronic use or a single high-level exposure generally causes permanent
damage, the clinical manifestations of which often intensify with age.
Exposure to neurotoxic heavy metals such as lead and mercury in
adulthood is less damaging than during brain development, but it is
unclear whether reducing exposure and body loads completely reverses
the symptoms. "Painter's Encephalopathy" and "Mad Hatter's Syndrome"
(from mercury exposure) reflect occupational exposure to neurotoxic
substances.
http://envirohealthhouston.org/concerns/neuro.html  "

In view of this, I don't know how some long term manifestations which
are reversible can come under neurological changes/damages?