Android : Threads started with activity Go to Wait Status After Activity Has Finished

i have a problem with my memory management, appearantly whenever i start an activity , 4 x new threads start with it and and whenever i close it those threads go to wait status :

78  20587   Wait    0   0   Thread-2349 
79  20515   Wait    0   0   Thread-2301 
80  20516   Wait    0   0   Thread-2302 
81  20517   Wait    0   0   Thread-2303 

and after afew times opening and closing it i have like 90x of threads in wait status, and my heap grows by 2k(very small) equal to before starting the Activity, i need to know is this some thing normal or it is a memory leak? if its so how can i trace it ? thanks alot