A total of 40 plant samples, including ryegrass (Lolium perenne,
n = 35) and mustard greens (Brassica juncea, n = 5) were collected.
All samples were placed in plastic bags during transport to the
laboratory. At the laboratory, plant samples were washed with tap
water and thoroughly rinsed with distilled water using a brush to
remove all traces of dust and soil from the roots and shoots. Both
root and shoot samples were dried at 40 °C until constant weight,
as several authors agree that this temperature can be applied to
avoid loss of mercury due to volatilization (Kamal et al., 2004;
Loredo et al., 2003), and milled.