Organic Sunscreen Contaminants at Depths in Mexico’s Riviera Maya Sinkholes (Cenotes)

The Yucatan Peninsula's limestone (karst) along with the area's inclement climate allows for quick groundwater recharge during large precipitous events. This rapid infiltration into the karst aquifer allows for contaminants of all kinds to be swept into the peninsula's main source of drinking water, whether from surface runoff or sinkholes (cenotes). Organic chemical sunscreens protect our skin by absorbing light and converting solar rays into non-damaging heat. When tested, these UV filters have been shown to bioaccumulate in various aquatic animals and freshwater bodies. As tourism increases in the Riviera Maya area of the Yucatan Peninsula, tourists have begun to flock inland to participate in activities involving the area's abundant cenotes, likely increasing the water's levels of chemical sunscreens. Previous research into sunscreen contamination in cenotes has shown increased presence of organic UV filters in these freshwater bodies. However, less research has been conducted to analyze trends within deeper cenotes, some of which pass through the saltwater halocline below the karst aquifer. Samples from two cenotes were collected, with one of the cenotes crossing the halocline at 50 m depth. It is hypothesized that there will likely be a decrease in organic UV filter concentrations with depth and that there would be higher concentrations in the freshwater than in the saltwater. This would be due to the organic material not passing through the denser saltwater layer. Our preliminary results have shown two organic sunscreen contaminants, Phenylbenzimidazole Sulfonic Acid (PBSA) and Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB), present at nearly all depths, with higher concentrations at and around the halocline layer of the 85 m deep cenote. Analyzing sunscreen contaminants at different depths within cenotes, specifically those with freshwater and haloclines, can offer a new perspective on sunscreen contamination and general pollution, given increasing human activity, development, and the need for clean drinking water in the region.尤卡坦半岛的石灰岩（喀斯特，karst）地貌与区域严酷的气候特征，使得强降水事件期间可实现快速地下水补给。这种快速渗入喀斯特含水层的过程，会将各类污染物冲刷进入该半岛的主要饮用水水源——无论污染物来自地表径流还是落水洞（天然井，cenotes）。 有机化学防晒霜通过吸收光线并将太阳辐射转化为无害热量的方式保护皮肤。经实验验证，这类紫外线过滤剂已被证实会在多种水生动物及淡水水体中发生生物富集。 随着尤卡坦半岛玛雅里维埃拉（Riviera Maya）地区旅游业的发展，游客开始大量前往内陆参与依托当地丰富天然井的活动，这可能会提升水体中化学防晒霜的含量水平。此前针对天然井中防晒霜污染的研究已证实，这类淡水水体中有机紫外线过滤剂的检出量有所上升。但目前针对深层天然井的污染变化趋势研究仍较为匮乏——部分深层天然井会穿过喀斯特含水层下方的咸水盐跃层（halocline）。 本研究采集了两处天然井的水样，其中一处天然井在50米深度处穿过盐跃层。研究假设：有机紫外线过滤剂的浓度会随深度增加而降低，且淡水中的浓度会高于咸水；这是因为有机物质无法穿过密度更高的咸水层。 我们的初步研究结果显示，两种有机防晒霜污染物——苯基苯并咪唑磺酸（Phenylbenzimidazole Sulfonic Acid，PBSA）和二乙氨基羟苯甲酰基苯甲酸己酯（Diethylamino Hydroxybenzoyl Hexyl Benzoate，DHHB）——在几乎所有深度的水样中均有检出，且在85米深天然井的盐跃层及其附近区域浓度更高。 考虑到该地区人类活动与开发程度不断提升，且对清洁饮用水的需求日益迫切，对天然井不同深度（尤其是存在淡水与盐跃层的天然井）中的防晒霜污染物展开分析，能够为防晒霜污染及一般性污染研究提供全新视角。