They certainly can.
Between 1992 and 1998, the Ministry of Public Health in Thailand carried out more than 2 million blood tests on farmers. More than 18% of the samples contained measurable amounts of pesticides. In some years, the number of blood samples containing pesticides was more than 25%.
In a more recent study carried out by Chiang Mai University, blood tests were carried out on people living in three farming communities. In one community, where fields and orchards surround the houses, more than two-thirds of the people had a risky or unsafe level of pesticides in their blood.
Some of these pesticides stay in the environment for many years, and can accumulate in the tissue of farm animals and humans. These chemicals are called “Persistent Organic Pollutants”, and DDT is a well-known example. Tests in Northern Thailand have shown that traces of DDT can be measured in the blood of villagers more than 10 years after the chemical was last used. This chemical is passed on to babies who are breastfed.