Occurrence and behavior of four of the most used sunscreen UV filters in a wastewater reclamation plant

Abstract

Four UV filters, benzophenone-3 (BP-3), 4-methylbenzylidence camphor (4-MBC), ethylhexyl methoxycinnamate (EHMC), and octocrylene (OC), have been examined along the different units of a wastewater reclamation plant (WWRP) located in Tianjin, North China. The analytical procedure included solid-phase extraction and gas chromatographic/mass spectrometric analyses. All four UV filters were detected in the influent during the three sampling campaigns (February, July, and September), and the concentrations ranged from 34 to 2128 ng L⁻¹. The concentrations of the four UV filters were higher in hot weather (July and September) than in cool weather (February). The monthly average removal ranged from 7.6% to 21% for the selected UV filters during coagulation–flocculation (C–F) treatment. The ozonation treatment achieved the maximum removal (16–28%); on the contrary, the continuous microfiltration (CMF) achieved the lowest removal (3.6–8.2%). The total removal efficiencies along the plant varied from 28% to 43%. These results indicate that the UV filters are not completely removed during WWRP treatment and may be carried over into the environment during the reuse applications.

Introduction

The growing awareness of the damage that ultraviolet (UV) radiation might cause on human health has led to increasing use of sunscreen products (sun creams, lotions, etc.). In order to protect consumers from UV radiation and to enhance light stability of the product, three to eight UV filters are usually added to sunscreen products. These chemicals are added to consumer sunscreen products in amounts up to 10% (Schreurs et al., 2002). UV filters are not only contained in increasing amounts in sunscreen products (Finkel, 1996) but also present now in many products of daily use, such as skin creams, cosmetics, hair sprays, body lotions, hair dyes, shampoos, and so forth. All of these belong to personal care products. Recently, there are increasing public concerns about secondary effects of pharmaceuticals and personal care products (PPCPs), because their ingredients may enter the aquatic environment and reach detectable and potentially harmful concentrations. As a result, organic UV filters have come into focus. The main characteristics of organic UV filters are the presence of single or multiple aromatic structures, often with attached hydrophobic groups. Most UV filters used in sunscreens are highly lipophilic and can therefore accumulate in the human body and the environment.

UV filters are applied superficially to the skin, and are designed to remain on the uppermost layers with minimal penetration. Although hydrophobic in nature, these substances have been recognized to undergo washing off from the skin surface in both laboratory and real-life investigations, thus being transferred to aqueous environments (Stokes et al., 1998; Stokes and Diffey, 1999) and reaching detectable concentrations. High lipophilicity of the UV filters has been shown to cause bioaccumulation in fish, leading to biological concentration of UV filters similar to those of polychlorinated biphenyls (PCBs) and dichloro-diphenyl-trichloroethane (DDT); for example, Nagtegaal et al. (1997) identified six different UV filters in fish in the Maarfelder Lake (Eifel, Germany), the total concentrations of which were 2.0 mg kg⁻¹ lipid in perch and 0.5 mg kg⁻¹ lipid in roach. Both fish species were contaminated with UV filters, PCBs, and DDT at similar levels. Furthermore, there are some concerns about UV filters due to their possible endocrine-disrupting effects. For example, Schlumpf et al. (2001) observed various estrogenic effects after in vitro and in vivo exposure to several UV filters. Schreurs et al. (2002) showed that UV filters can also bind to estrogen receptor β.

After being used, UV filters may enter the aquatic environment. Contamination of the aquatic environment with UV filters from sunscreen products may occur through two principal input pathways, namely, “direct inputs” from recreational activities (release from skin during swimming and bathing) and “indirect inputs” via wastewater treatment plants (WWTPs), for instance, rubbed off by towels, washed off during showering, or even from renal excretion after percutaneous or oral (lipsticks) uptake. Several studies have identified UV filters in wastewater and surface water. Balmer et al. (2005) examined the occurrence of four important organic UV filter compounds in wastewater and surface water in Switzerland. Poiger et al. (2004) compared predicted and measured UV filter concentrations in a regional mass balance study for two Swiss recreational lakes. Lambropoulou et al. (2002) determined 2-hydroxy-4-methoxybenzophenone and octyldimethyl-p-aminobenzoic acid at the ng mL^–1 level in water samples, such as swimming pool, shower waste, and seawater, from people who had applied cosmetic products to their skin prior to bathing. Up to now, most of the studies focused on UV filters have been carried out in Europe and the USA, whereas data from the countries in Asia are scarce. A lack of information should be dealt with to have a complete picture of the occurrence and fate of these compounds in the whole world, as well as to compare the situation in different areas. On the other hand, most of the investigations concern the occurrence of UV filters in surface waters and WWTPs; however, there is little information on the occurrence, behavior, and fate of UV filters in wastewater reclamation plants (WWRPs).

The aim of this work is therefore to investigate the behavior of the common UV filters along the different units of a wastewater reclamation plant located in Tianjin, China (a typical northern city with a population of 9 million). The removal efficiency from the water phase of each compound in each particular unit has been determined.

To gain an overview of the UV filters most frequently used in sunscreen products, we conducted a regional market survey and investigated the content of UV filters in the area of Tianjin. A total of 20 sunscreen products were purchased in 2004, including all of the most popular brands. According to the labels, we selected four of the most common organic UV filters that were contained in the 20 sunscreen products. They are listed in Table 1 together with their content and frequencies of occurrence in the selected sunscreen products.

The structure of the four UV filters, namely, BP-3 (2-hydroxy-4-methyl-benzophenone), EHMC (3-(4-methoxyphenyl)-2-propenoic acid 2-ethylhexyl ester), 4-MBC (3-(4′-methyl-benzylidene) bornan-2-one), and OC (2-cyano-3,3-diphenyl-2-propenoic acid 2-ethylhexyl ester), are given in Fig. 1. The octanol/water partition coefficients, log K_ow, are as follows: 3.8 for BP-3, 5.1 for 4-MBC, 6.0 for EHMC, and 6.9 for OC (Balmer et al., 2005).