You don't say where you
are located.Nor do you say how your bees were exposed.Was the actual hive sprayed or did they spray you neighbors dandylions?Try to get the name of the chemical used.You may be able to get compensation and the applicator could be fined.
Most states take bee kills by pesticides very seriously .In Mass,for instance,because of Covid 19,all bee inspections have been cancelled except for imports,Foulbrood and Pesticide kills.Contact you state inspector
(If you have one!) immediately.
Most bee kills come from direct exposure to the insecticide while foraging,next comes bee contact with previously sprayed floral resources,then with contaminated nectar and pollen brought back to the hive.
It is rare that hive parts are contaminated although you could have contaminated stores.
Too often beekeepers shout pesticide kill and then don't follow through.Sloppy pesticide applicators won't be stopped unless we make a big stink.Again, contact your state officials immediately.They need fresh samples.
(40+ years with a Supervisory Pesticide License while keeping bees)