Cadmium-Containing Quantum Dots Used in Electronic Displays: Implications for Toxicity and Environmental Transformations

Cadmium-containing quantum dot (QD) nanoparticles are integrated into electronic displays because of their ability to efficiently convert colors. There are conflicting accounts as to whether these particles present a hazard to the environment, as they have been studied either as (1) embedded QDs in display screen films or (2) as model QDs with small, hydrophilic ligands. Both approaches have limitations that we addressed by synthesizing QDs featuring the core-shell structure and the thick polymer coating present in commercial devices to probe the dissolution of QDs in response to two environmental factors (pH and dissolved oxygen) over 1 day and 6 months. Results show that QDs were chemically stable at circumneutral pH (0% Cd dissolution after 6 months), but low pH initiated rapid dissolution under both aerobic and anaerobic conditions (up to 100% Cd dissolution after 6 months). In addition to the presence of a capping polymer, the QD shell structure led to more chemically stable nanoparticles compared to nonshelled QDs, as the presence of ZnS shells decreased Cd dissolution by 75%. The dense aggregation of QDs into structures of similar to 100 nm diameter over time was observed as well, which could lead to decreased bioavailability. To test this, we used liver cells to compare the toxicity of pristine QDs to those subjected to acid dissolution. Our results reveal that low-pH-exposed QDs separated from dissolved ions are less toxic than pristine QDs (half maximal inhibitory concentration, IC50, of 290 and 150 mg/L, respectively) and suggest a key role of dissolved ions and capping polymers for QD toxicity. These findings highlight the use of a commercially relevant nanoparticle structure to demonstrate fate and toxicity.