Example, 100mg of a drug with a half-life of 60 minutes is taken:

High plasma protein binding limits the partitioning of xenobiotics from the blood into the tissues where they could be metabolized. This serves to extend the half-life of the xenobiotic as only free chemical may enter the metabolizing enzymes.

The half-life of a drug can be determined using the following equation: t1/2 = (0.7 x Vd) / Cl, where Vd is volume of distribution and Cl is clearance.

2 & 3. CBC, Creatinine, plasma antioxidants, alkaline phosphatase, SGPT, serum albumin, 

1. This is done routinely for registered pharmaceuticals and food. Half life calculations at a range of temperatures is feasible. PPM can be determined over time and temperature gradients. Biological monitoring can be done in meat, milk, eggs, blood of livestock (especially   poultry, eggs,  piglets for drugs/ toxins transmitted to foetus during pregnancy, dairy cows for milk tests ) . You can also  test lab animals including guinea pigs, rats, mice,  and fish. 
2. Human blood tests exist to monitor blood levels of various chemicals ( blood alcohol is well known, but toxic chemicals  as well up to PPM for things like DDT.) If you have a new chemical/drug you want to test in humans it is VERY difficult to get ethics clearance. Look at what happened with the COVID-19 vaccine!!!!  Environmental poisons where people are exposed are easier, you can take blood from people exposed to the toxin to determine PPM. You can also monitor health with routine  tests of serum and whole blood with an anticoagulant. Blood can be drawn by a registered nurse   or doctor. Animal blood can be drawn by a registered vet nurse or vet or animal health technician working with experimental animals.
PCR's  can be done for biological agents ( eg infectious diseases and parasites). We have desktop faecal PCR's available for pet dog   diseases like parvo-virus and cryptosporidium.  For humans - there are OTC PCR tests available for COVID-19. Put a swab up your nose and have the answer in  a few minutes. 

please rephrase your question 1, its not clear what you are referring

2. CBC, Full biochemical profile, and antioxidants system. LFT, RFT. cancer markers panel
3. depend on the toxin and organs affected

It is often not necessary to use invasive blood draws as depending on the material(s) of interest there are robust data for urinary biomonitoring.  There is perhaps no greater resource for this that the ACGIH Biological Exposure Indices.