Photolysis characteristics and influencing factors of adenosine 5′-monophosphate in seawater

Environmental context Organophosphorus (OP) is bioavailable to phytoplankton with photolysis can play an important role in the process. The photolysis behaviour of an OP (adenosine 5′-monophosphate, AMP) in seawater was investigated, and AMP can release inorganic phosphate under environmentally relevant light conditions, indicating OP photodegradation might be important in the phosphorus biogeochemical cycle. The results are helpful to further understand the bioavailability and cycle of OP in marine environment.Rationale Organic phosphorus (OP) is a potential source of bioavailable phosphorus for phytoplankton through photolysis and other degradation processes. Therefore, OP photodegradation plays an important role in phosphorus biogeochemical cycle.Methodology Taking adenosine 5′-monophosphate (AMP) as a model OP, we investigated the photolysis behaviour in seawater and discussed the mechanism. The photolysis dynamics were studied based on the inorganic phosphorus production at appropriate time intervals, which was analysed by spectrophotometric molybdenum blue method. The effects of medium, light and radicals were investigated.Results It was found that AMP can release inorganic phosphate under photosynthetically active radiation and ultraviolet (UV) with UVB being the most reactive band. The degradation of AMP in seawater was lower than that in deionised water under the same conditions, and the fresh seawater was more beneficial than aged seawater. The kinetics could be described by apseudo-first order equation. Fe3+ can promote the photolysis due to the generation of ·OH radicals, while within the range of this study, changes of Fe3+ content have no substantial effect on the promotion. The influence of ethanol and tetrahydrofuran as radical inhibitor showed evident inhabitation to the degradation, indicating that ·OH and 1O2 played an important role in the process, and ·OH seemed more important than 1O2.Discussion OP photodegradation is of importance in the phosphorus biogeochemical cycle. Varying properties of the medium and light can affect the OP transformation in seawater. The results are helpful to further understand the bioavailability and cycle of OP in the marine environment.