Mapping the Photochemistry of European Mid-Latitudes Rivers: An Assessment of Their Ability to Photodegrade Contaminants

Abstract

The abiotic photochemical reactions that take place naturally in sunlit surface waters can degrade many contaminants that pose concern to water bodies for their potentially toxic and long-term effects. This works aims at assessing the ability of European rivers to photoproduce reactive transient intermediates, such as HO• radicals and the excited triplet states of chromophoric dissolved organic matter (3CDOM*), involved in pollutant degradation. A photochemical mapping of the steady-state concentrations of these transients was carried out by means of a suitable modeling tool, in the latitude belt between 40 and 50°N. Such a map allowed for the prediction of the photochemical lifetimes of the phenylurea herbicide isoproturon (mostly undergoing photodegradation upon reaction with HO• and especially 3CDOM*) across different European countries. For some rivers, a more extensive dataset was available spanning the years 1990–2002, which allowed for the computation of the steady-state concentration of the carbonate radicals (CO3•−). With these data, it was possible to assess the time trends of the photochemical half-lives of further contaminants (atrazine, ibuprofen, carbamazepine, and clofibric acid). The calculated lifetimes were in the range of days to weeks, which might or might not allow for efficient depollution depending on the river-water flow velocity.

Prediction of Photochemically Produced Reactive Intermediates in Surface Waters via Satellite Remote Sensing

“…Thus, models are often used to predict the photochemical lifetimes of pollutants. For example, Carena and Vione conducted modeling work and map the formation of PPRIs in European mid-latitudes rivers to gain insight into the photodegradation kinetics of water pollutants. Zeng and Arnold investigated the photodegradation of pesticides in surface waters and estimated the second-order rate constants for their reactions with PPRIs .…”

Evaluation of the Environmental Fate of a Semivolatile Transformation Product of Ibuprofen Based on a Simple Two-Media Fate Model

“…Details about the modeling procedure are reported in Text S2. It was considered a reasonable 2 m deep water column, while DOC ranged from <1 to ∼10 mg C L –1 (nitrate and nitrite were not included in the model, because such data are lacking, which might slightly underestimate photoreaction kinetics) . It is suggested that IBAP volatilization from surface-water environments to the gas phase is potentially quite significant as it may approach up to 25% for the considered scenarios.…”

The Possible Production of Harmful Intermediates Is the “Dark Side” Of the Environmental Photochemistry of Contaminants (Potentially Adverse Effects, And Many Knowledge Gaps)

“…This method could also open up the way to the definition of environmental vulnerability, in the context of photochemical reactions. 4 Currently, photoreaction pathways are well-known for only a small selection of contaminants. Moreover, the characterization and quantification of the formation yields of intermediates faces several challenges, which include the following:…”

“…Maps of the formation yields in sunlit river water of (left) 10,11-dihydro-10,11-trans-dihydroxycarbamazepine from carbamazepine, and (right) 4-chlorophenol from clofibric acid. The calculation procedure is described in previous work . Many sites of central-southern France have the highest potential to produce the former intermediate, and the lowest potential to produce the latter.…”

“…Such vulnerable water bodies should be prioritized for the assessment and environmental impact of parent contamination. This method could also open up the way to the definition of environmental vulnerability, in the context of photochemical reactions …”