Colony forming units mL⁻¹ of <i>E.coli</i> on TS agar plates following exposure to a sterile deionized water control, and treatments of 2.0, 2.5 and 3.1 nm-sized Pd NPs and Pd²⁺ ions.

<p>Exposure times are within 5 minutes of exposure (0 h), and after 4 h, 8 h and 24 h (horizontal). The concentration range of each of the Pd NPs and Pd²⁺ tests were from 10⁻⁴–10⁻⁹ M (vertical). Significant differences shown in the figure represent comparisons between the four test chemicals using One-Way ANOVA and do not include comparison to the control (white bar); significance is represented by lowercase letters. Significance was assessed at α = 0.05. Capitalized letters refer to individual sub-figures A–X, as corresponds to exposure time and concentration.