Yes it will exhibit a half-life, but it will be very condition dependent, I suggest you do some simple experiments to determine the value under your conditions, because a value determined by others will not match yours unless all the relevant variables are close to identical. It is of course possible that the loss in LDH activity will follow more complex kinetics but first order or pseudo-first order kinetics are a reasonable assumption to start with. Good luck, Phil.
Yes, the half-life of LDH that has been released from cells into the surrounding medium is approximately 9 hours. You will have to optimize the test exposure period. If the exposure period is greater than 9 hours, the quantity of active LDH remaining at the end of the experiment may be under estimated.