Occurrence and spatial distribution of paralytic shellfish toxins in seawater and marine organisms in the coastal waters of Qinhuangdao, China.

In recent years, paralytic shellfish toxins (PSTs) have been prevalent in the coastal waters of Qinhuangdao, the west coast of the Bohai Sea, China. The content of PSTs in shellfish often exceeded the regulatory limit of 800 µg STX equivalent (eq.) kg-1, which poses a serious threat to human health. In this study, two surveys were conducted in May 2021 and May 2022 to investigate the distribution of PSTs in the coastal waters of Qinhuangdao. Seawater, surface sediment, phytoplankton, zooplankton, and other marine organism samples were collected, and the composition and concentration of PSTs were analyzed by liquid chromatography with tandem mass spectrometry (LC-MS/MS). Results showed that multiple PST components were detected in all seawater samples collected at different depths, mainly including GTX1/4, GTX2/3, dcGTX2, STX and C1/2, and the highest concentration of PSTs reached 244 ng STX eq. L-1. The sediment samples also contained low levels of C1/2 and GTX2/3. Trace amounts of C1/2 and GTX1-4 were detected in phytoplankton and zooplankton. Moreover, all bivalve shellfish samples were found to contain PSTs, and the scallop Azumapecten farreri and the ark clam Anadara kagoshimensis showed relatively high concentrations of 607 and 497 µg STX eq. kg-1, respectively. In addition, low levels of PSTs were also found in some non-traditional PST vectors, including whelk Rapana venosa, octopus Amphioctopus ovulum, goby Ctenotrypauchen chinensis, and greenling Hexagrammos agrammus. Results of this study improve the understanding of the distribution of PSTs in seawater and marine organisms and the potential risk of persistent PSTs in seawater to marine ecosystems and human health.

Bioaccessibility of paralytic shellfish toxins in different cooked shellfish using the simulated digestive model.

Current regulatory limit values for paralytic shellfish toxins (PSTs) in shellfish products are not considering the bioaccessibility of PSTs in seafood matrix during the gastrointestinal digestion for human beings. In this study, the bioaccessibility of PSTs in the shellfish cooked by different ways was assessed using a static in vitro human digestion model. Results showed that the dissolution of PSTs from shellfish tissues was not significantly affected by digestion time, ratios of solid weight to liquid volume (S/L) and cooking methods, but obviously facilitated by digestive enzymes. Different cooking ways reduced the contents of PSTs in shellfish by 45% to 88%, but did not significantly change the high bioaccessibility of PSTs that ranged from 80% to 95% in four different shellfish matrices. Transformation or degradation of PSTs occurred during the simulated digestion process. This work will help us to objectively assess the potential risks of PSTs to human health.

Phosphorous Retention and Release by Sludge-Derived Hydrochar for Potential Use as a Soil Amendment.

To solve both the problems of P deficiency in arable soil and excessive waste sludge disposal, we evaluated hydrothermal carbonization of sludge with the aim of recycling sludge P resources for soil amendment. In contrast with pyrochars obtained through pyrolysis, hydrochars generated from hydrothermal carbonization often feature variable properties and therefore require detailed characterization. In this study, sludge-derived hydrochars were evaluated to determine their P content and fractionation, release and availability of P, and P adsorption and desorption behavior. We also assessed changes in P availability after soil was amended with the hydrochars. Our results showed that the chars were rich in total P (up to 25,175 mg kg), but most of the free fractions were transformed to bound fractions, thereby reducing the available P concentrations. However, available P content was >417 mg kg, which was far higher than soil demand. The hydrochars shifted from releasing to adsorbing P adsorbent when the environmental P concentration increased above 20 mg L. The hydrochars showed a high phosphate adsorption capacity (up to 23,815 mg kg) and the adsorbed P could be readily released. The addition of 1% P-laden hydrochar significantly enhanced the soil available P content by 8.93 mg kg. These findings have important implications for further development of hydrochar-based P carriers as a slow-releasing fertilizer.