The Effects of Sunscreen on Cyanobacteria

Ultraviolet-filters found in various manufactured cosmetic products have been detected recently as environmental contaminants at trace concentrations. The effects of these low levels of sunscreen products on cyanobacteria were investigated in this study. Average trends of triplicate conditions in this study suggest that sunscreen causes decreased scytonemin and chlorophyll a production, as well as decreased rates of photosynthesis, in Calothrix sp. (PCC 7102) over short time scales. At the community scale, clone library analyses indicate that cyanobacterial community composition was not significantly affected by the addition of sunscreen to the enrichment cultures. Introduction A variety of commercially-available cosmetic products contain ultraviolet-filters, which are compounds designed to absorb UV light (5). Due to the widespread use of sunscreen agents, researchers have begun studying the occurrence and fate of these compounds in the environment. UV-filters raise concerns because, unlike many other compounds in the pharmaceutical and personal care product (PPCP) category of trace pollutants, they are directly input into the aqueous environment in addition to input as wastewater treatment plant effluents. For example, recreational swimming can directly input UV-filters into the environment, thereby allowing the compounds to evade potential biodegradation or physical-chemical methods of removal during wastewater treatment (2). One occurrence study of two Swiss lakes used for recreational swimming found that the highest concentration detected was 125 ng/L for the compound benzophenone-3 (5). Another study examined Swiss lakes and a river and found concentrations ranging from <2 ng/L to 35 ng/L for UV-filters benzophenone-3, 4-methybenzylidene camphor, ethylhexyl methoxy cinnamate, and octocrylene (1). Compared to pharmaceuticals also in the PPCP category, relatively little is known about the effects of the sunscreens on nontarget organisms (2). The nontarget organisms of interest in this study are the cyanobacteria. UV light has high energy levels that can damage DNA, proteins, and other important molecules in bacteria. Bacteria exposed to damaging UV rays have various mechanisms to overcome the damage that could lead to survival, growth, pigmentation, photosynthesis, and motility problems. In addition to repairing UV damage, some are also able to produce carotenoids, detoxifying enzymes, radical quenchers, antioxidants, and substances capable of absorbing or screening UV light. One of these UV-screeners and absorbers is scytonemin (7). Scytonemin is a pigment found in the sheath of more than 300 cyanobacteria and is yellowish-brown in color. This compound is thought to be unique to cyanobacteria (6) It is a proposed screening compound for UV-A and has shown to be induced by cyanobacterium exposure to UV-A (6, 7). This study aimed to elucidate the effect of sunscreen at environmentally relevant concentrations on cyanobacteria. It was hypothesized that the presence of UV-filters in the waters surrounding cyanobacteria would benefit the bacteria by protecting them from harmful UV light, therefore allowing them to have increased photosynthesis rates and chlorophyll a production, and decreased need for scytonemin production. It was also predicted that environmental communities of cyanobacteria would shift after exposure to UV light depending on whether or not they were amended with sunscreen. Experiments were conducted on both an individual cyanobacteria strain, Calothrix sp. (PCC 7102), and on environmental samples collected from beach sand. Materials and Methods