Thioguanine

Despite health benefits, fish consumption poses risks of exposure to toxic substances. Concentrations of toxic metals were determined in 20 fish species available on the Polish market. Cadmium (Cd) concentrations were within the range 0.003-0.005 mg/kg, lead (Pb) 0.011-0.033 mg/kg, total mercury (THg) 0.014-0.133 mg/kg, methylmercury (MeHg) 0.010 mg/kg - 0.108 mg/kg, inorganic arsenic (iAs) below 0.02 mg/kg. Mercury and methylmercury in tuna were at higher levels. The average contents 0.919 mg/kg and 0.684 mg/kg, were close to the limit for THg 1 mg/kg (Commission Regulation (EU) 2023/915). Risks to consumer health were estimated on the base on toxicity markers non-carcinogenic (THQ) for Cd, Pb, MeHg and iAs, and carcinogenic (CR) coefficient for iAs. Values THQ were low for Cd (0.5 x 10^-3 - 2 x 10^-3), Pb (0.7 x 10^-3 - 2.4 x 10^-3), MeHg (2.8 x 10^-2 - 31 x 10^-2) and for iAs (1.9 x 10^-2). The CR marker for iAs was also low at 0.86 x 10^-5. Low values for toxic metals and toxicity markers in fish from the Polish market confirms their safe consumption. Only in tuna the marker THQ for MeHg was twice the recommended safe value. The high methylmercury contents and high THQ in tuna indicates limitations in consumption this fish. Over the past decade, levels of toxic metals in fishes on the Polish market have remained stable. The only significant change was the increased THg and MeHg in tuna.

Mercury pollution in Minamata Bay has remained a persistent environmental issue since the discovery of Minamata disease. In this study, hydrodynamic simulations were performed using Delft3D FLOW, and a mercury transformation model was developed with the OPEN PLCT module of the WAQ system. A precipitation-related freshwater inputs module was incorporated to capture the direct impact of precipitation on the water surface. The simulated concentrations of total dissolved mercury (THg) were generally consistent with field observations, supporting the reliability of the model. After intense rainfall, surface water THg levels increased sharply, likely due to the direct influence of precipitation on the water column. Simultaneously, salinity at the bottom decreased, which coincided with elevated THg levels near the sediment. The behavior of methylmercury (MeHg) was more complex. A Decision Tree Regressor analysis revealed that salinity and water temperature were the main drivers of the MeHg to THg ratio (MeHg/THg). The highest MeHg/THg proportion (67.7 %) was observed when salinity dropped below 26.5 ‰, around a temperature of 20 °C. Moreover, under conditions of high dissolved oxygen (DO >6.05 mg/L) and elevated total organic carbon (TOC > 4.408 mg/L), the average MeHg/THg ratio reached 27.9 %, suggesting that oxygen-rich environments with sufficient organic substrates may facilitate mercury methylation. These findings provide new insight into how direct precipitation events and water column properties jointly influence mercury cycling in estuarine systems.