Modelling the release, dispersion and fate of nanoparticulate titanium dioxide from sunscreen products in recreational lakes

二氧化钛纳米粒子（n-TiO2）对水生生态系统的威胁越来越大，因为它们的持久性和在洗浴季节从休闲水域的防晒霜中直接释放出来。但是，它们的影响仍然难以评价，因为一方面，监测它们在环境介质中的浓度的分析方法直到最近才发展起来。另一方面，它们在水生系统中的命运仍然没有得到充分的了解。特别是，表面微层（SML）、散装水、沉积物、植物和浮游生物之间的分布取决于实验室实验中单独研究的各种机制，但很少在环境条件下进行评估。此外，尽管风对疏水n-TiO2的空间分散有重要作用，但目前还没有研究风在SML中纳米颗粒分散中的作用。在本项目中，我们建议调查n-TiO2在典型休闲湖泊中的分布，并基于详细的经验数据，评估描述其命运的反应输送模型。我们将通过对沐浴者的调查和样本来量化和表征防晒霜的输入，并通过专门的实验确定在现场条件下防晒霜从皮肤上的冲洗率。n-TiO2在水相、地表水（疏水膜）和水生生物中的含量将使用一种新开发的方法来测定，该方法依靠微量元素来校正天然tio2背景。将进行高测量频率的采样活动，以获得SML上对流和风漂移引起的色散率的经验数据。通过监测沐浴季节前后沉积物中人为n-TiO2的浓度来确定沉积物中n-TiO2的积累情况。获得的数据将用于开发、测试和优化命运分布模型，该模型考虑了对流和风引起的空间分散以及纳米粒子的性质和水化学。将进行功能分析，以确定命运模型所需的参数。使用从防晒霜中提取的n-TiO2，并在湖水中自然涂覆，来确定附着效率。将根据对研究湖中胶体的详细调查选择天然胶体的替代品，并将其用作功能分析中的异聚集伙伴。为了将风对遮光剂的影响参数化，将进行水槽中观实验，在空气动力和水动力控制条件下，对遮光剂的稳定性进行测试。该结果将使我们能够确定娱乐水域中防晒霜中n-TiO2命运的最相关过程，从而为更准确地评估防晒霜中无机紫外线过滤器的生态风险打开大门。

Titanium dioxide nanoparticles (n-TiO2) represent an increasing threat for aquatic ecosystems due to their persistence and the direct release from sunscreens in recreational waters during the bathing season. However, their impact is still difficult to evaluate because, on one side, analytical methods for monitoring their concentration in environmental media have been developed only recently. On the other side, their fate in aquatic systems is still insufficiently understood. In particular, the distribution between the surface microlayer (SML), bulk water, sediments, plants, and plankton depends on various mechanisms that were investigated individually in laboratory experiments, but were rarely assessed under environmental conditions. Furthermore, the role of wind in the dispersion of nanoparticles present in the SML has not been investigated so far, although it is expected to contribute significantly to the spatial dispersion of hydrophobic n-TiO2. In this project, we propose to investigate the distribution of n-TiO2 in a typical recreational lake and, based on detailed empirical data, assess a reactive transport model describing their fate. We will quantify and characterize the input of sunscreens using surveys and samples among bathers and determine the wash-off rate of sunscreen from the skin under field conditions using dedicated experiments. The amount of n-TiO2 in the water phase, in the surficial water (hydrophobic films), and in aquatic organisms will be determined using a newly developed method relying on trace elements to correct for the natural TiO2-background. A sampling campaign at a high measurement frequency will be conducted to obtain empirical data on the dispersion rate due to convection and wind drift on the SML. The accumulation of anthropogenic n-TiO2 in the sediment will be determined by monitoring the concentration before and after the bathing season. The obtained data will be used to develop, test, and optimize fate distribution models taking into account spatial dispersion due to convection and wind together with the nanoparticles’ properties and the water chemistry. Functional assays will be carried out for determining the parameters required for the fate model. Attachment efficiencies will be determined using n-TiO2 extracted from sunscreen and coated naturally in lake water. Surrogate for natural colloids will be selected based on a detailed investigation of the colloids in the study lake and used as heteroaggregation partners in the functional assays. To parametrize the effect of wind on the SML, flume mesocosm experiments will be conducted to produce and test the stability of sunscreen SML under controlled aero- and hydrodynamic conditions. The results will enable us to determine the most relevant processes involved in the fate of n-TiO2 from sunscreens in recreational waters and, thereafter, open the door to more accurate ecological risk assessment of inorganic UV-filter in sunscreens.