QUANTUM DOTS EXHIBIT LESS BIOACCUMULATION THAN FREE CADMIUM AND SELENIUM IN THE EARTHWORM EISENIA ANDREI DAVID T.R. STEWART,KATIA NOGUERA-OVIEDO,VINCENT LEE,SARBAJIT BANERJEE, DAVID F. WATSON, and DIANA S. AGA* Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York, USA (Submitted 24 October 2012; Returned for Revision 5 December 2012; Accepted 10 January 2013) Abstract: The present study addresses the bioaccumulation behavior of cadmium selenide quantum dots by Eisenia andrei earthworms in a terrestrial environment. Earthworms were exposed to quantum dot-treated soil for up to 4 wk and analyzed for cadmium and selenium concentration using inductively coupled plasma mass spectrometry. Results were compared with those from earthworms exposed to cadmium nitrate and selenious acid, as positive controls, and those exposed in untreated soil (negative control). Earthworms exposed to quantum dots showed significant bioaccumulation of cadmium and selenium (5.3- and 1.5-fold higher concentration over negative controls, respectively) after 4 wk. Over the same 4 wk, positive control earthworms accumulated 9.2- and 2.2-fold higher cadmium and selenium, respectively, than negative controls for a much more substantial final body burden of the 2 elements. The concentrations also increased with exposure time; cadmium concentrations increased from 3600  310 ng/g to 8080  660 ng/g, from 1 to 4 wk, suggesting that further bioaccumulation may take place with even longer exposure time. The molar ratio of cadmium to selenium in the quantum dot- exposed worms (6.2) is closer to the ratios seen in positive control worms (7.2) than to the pure quantum dots (1.8), which implies that quantum dots are taken up predominantly in the degraded form. The results suggest that chemical modification of quantum dots to protect them from environmental degradation could potentially reduce bioaccumulation of the nanoparticles by earthworms. Environ Toxicol Chem 2013;32:1288–1294. # 2013 SETAC Keywords: Quantum dots Bioaccumulation Earthworm Nanotoxicology Cadmium INTRODUCTION Engineered nanomaterials, which are materials with at least 1 dimension between 1 and 100 nm, have found a wide range of applications in agriculture, energy production, electronics, drug delivery, and medical diagnostics. The anticipated increase in production of engineered nanomaterials has prompted govern- ment agencies and scientists to investigate the environmental fate and behavior of these materials to understand their potential risks to humans and other organisms after exposure [1]. An example of an engineered nanomaterial with many promising applications is quantum dots, which exhibit size-dependent light absorption and emission properties [2,3] that make them ideal for use as photoluminescent biomarkers and photovoltaic sensitizers [4–8]. Quantum dots are typically composed of a cadmium selenide crystalline core with an organic ligand coating; they have complex behaviors in environmental and biological matrices [9–13]. Commercial products containing quantum dots are being developed and are expected to be on the market soon. However, disposal of these products after their intended use will most likely lead to the release of quantum dots in the environment [14]. The behavior of quantum dots in the terrestrial environment requires further study to understand the potential risks associated with waste products containing quantum dots, and to develop mitigation strategies that can minimize deleterious environmental effects [1,14]. In the present study Eisenia andrei was used as a model organism to determine the bioaccumulation of quantum dots relative to free metals in soil. Eisenia andrei is an oligochaete earthworm that has been used for decades in soil toxicity tests [15–18], including a variety of standardized tests developed by the US Environmental Protection Agency (USEPA) [19], the Organization for Economic Cooperation and Development (OECD) [20,21], and Environment Canada [22]. Earthworms are ideal models for soil organisms because of their prevalence and importance in the environment, and the relative ease of maintaining them in a laboratory culture. Recent studies have assessed the bioaccumulation of carbon nanotubes [18,23], gold nanoparticles [17,24], copper nanoparticles [25], aluminum oxide nanoparticles [15], and a range of metallic and metal oxide nanoparticles [26] by earthworms. Particle size, surface functionality, and exposure media have been shown to affect the bioaccumulation behavior of nanoparticles [27]. Effects on reproduction and gene regulation have been observed on earthworms exposed to gold and copper nanoparticles [17,25], but mortality has not been reported even with high concen- trations of nanoparticles. Avoidance of aluminum oxide nanoparticles [15], titanium dioxide nanoparticles [27], and silver nanoparticles [28] has been observed as well. The toxicity of quantum dots to cell cultures and laboratory rodents [29], aquatic invertebrates [30–32], and fish [33] has been investigated; however, studies involving soil organisms have not kept pace. The specific reproductive effects of quantum dots were observed in nematodes exposed to growth media [34], but studies have not been published showing bioaccumulation of quantum dots from soil. Earthworms are known to bioaccumu- late metals [35] but are tolerant to doses of cadmium as high as 40 mg/g (reproduction endpoint [16]). Therefore, acute toxicity tests are not relevant for assessing the potential environmental impacts of quantum dots at concentrations that may be expected in the environment, which would be much lower than the lethal dose for cadmium. Bioaccumulation of quantum dots has been observed in other organisms [30–33,36] but has not yet been studied in E. andrei. Earthworms with high body burdens of *Address correspondence to dianaaga@buffalo.edu. Published online 15 February 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/etc.2182 Environmental Toxicology and Chemistry, Vol. 32, No. 6, pp. 1288–1294, 2013 # 2013 SETAC Printed in the USA 1288