Trace metal phytotoxicity in solution culture: a review

Area of Science:

• Environmental Science
• Plant Science
• Toxicology

Background:

• Solution culture is widely used to assess trace metal phytotoxicity.
• A comprehensive literature review (1975-2009) analyzed 119 studies on plant responses to As(V), Cd(II), Co(II), Cu(II), Hg(II), Mn(II), Ni(II), Pb(II), and Zn(II).
• Significant variability in reported toxic concentrations (five orders of magnitude) highlights the need for standardized methodologies.

Purpose of the Study:

• To evaluate the phytotoxic effects of common trace metals on plants grown in solution culture.
• To establish a relative toxicity ranking of these metals.
• To propose methodological improvements for future phytotoxicity studies.

Main Methods:

• Systematic literature review of studies published between 1975 and 2009.
• Selection of 119 studies based on criteria ensuring valid comparison of results.
• Analysis of reported toxic concentrations and plant responses across various species and conditions.

Main Results:

• The phytotoxicity ranking of trace metals was determined as: Pb ≈ Hg > Cu > Cd ≈ As > Co ≈ Ni ≈ Zn > Mn.
• Median toxic concentrations (µM) were reported: Pb (0.30), Hg (0.47), Cu (2.0), Cd (5.0), As (9.0), Co (17), Ni (19), Zn (25), and Mn (46).
• Wide variation in reported toxicities underscores experimental inconsistencies.

Conclusions:

• Standardized protocols are crucial for reliable trace metal phytotoxicity data.
• Recommendations include using dilute solutions mimicking soil solutions, monitoring and reporting pH and metal concentrations, assessing pH influence on speciation, and using appropriate exposure durations and plant variables.
• Adherence to these guidelines will improve the accuracy of growth depression and metal concentration relationships.