Straw return decreases polycyclic aromatic hydrocarbon (PAH) accumulation in winter wheat and human health risk by enhancing PAH dissipation in rhizosphere soil

Straw return in situ,a common agronomic measure in China,has been widely used not only to increase crop yields and improve soil nutrients but also to remove polycyclic aromatic hydrocarbons(PAHs)from agricultural soils.Nevertheless,the safety risks of food crops(i.e.,human health risk of wheat grains)grown in PAHs-contaminated agricultural soils amended with crop straw remain uncertain.A pot experiment was conducted in a PAHs-contaminated agricultural soil cultivated with winter wheat under different ratios of corn straw addition(0%(control,CK),1%,2.5%,and 5%,weight/weight).Results showed that corn straw addition significantly(P<0.05)decreased PAH concentrations in rhizosphere soil,roots,straws,and grains by 48.32%–50.01%,11.85%–42.67%,9.78%–28.03%,and 14.16%–31.67%,respectively,compared with CK,whereas the transfer factors of PAHs from roots to straws were significantly(P<0.05)increased.A correlation heatmap showed that PAH concentrations in roots,straws,and grains were positively(P<0.01)correlated with those in rhizosphere soil.These indicated that corn straw decreased PAH accumulation in winter wheat due to the increase of PAH dissipation in the rhizosphere soil,although it enhanced PAH transfer in winter wheat.The incremental lifetime cancer risk(ILCR)model indicated that corn straw significantly(P<0.05)decreased the human health risk of winter wheat grains by 29.73%–45.05%.Overall,corn straw apparently reduced PAH accumulation in winter wheat,ecological risk,and human health risk via enhancing PAH dissipation in the rhizosphere soil.These findings provide an important scientific basis and theoretical guidance for agricultural safety production.

Biochar reduces uptake and accumulation of polycyclic aromatic hydrocarbons(PAHs) in winter wheat on a PAH-contaminated soil

For years, biochar has been successfully used for the remediation of polycyclic aromatic hydrocarbons(PAHs) in contaminated soils, not only for improving their removal from soil but also for reducing their uptake by crops. However, the underlying mechanism of biochar application reducing PAH uptake and accumulation in winter wheat remains unclear. Pot trials were conducted on a PAH-contaminated soil amended with bamboo biochar, coconut shell biochar,and maize straw biochar(MSB) for an entire growth period of winter wheat. Compared with no biochar control(CK), application of the three types of biochar significantly(P < 0.01) reduced grain PAH concentration, total equivalent concentration(TEC), and incremental lifetime cancer risk(ILCR), indicating that biochar application, especially MSB, reduced the risk of exposure to PAHs in wheat grain. Furthermore, all three types of biochar significantly(P < 0.05)reduced PAH uptake and accumulation in wheat roots and stems, probably because biochar application enhanced the degradation of PAHs in the rhizosphere soil. Compared with CK, application of the three types of biochar significantly(P < 0.05) reduced the concentration of PAHs in the rhizosphere soil by15.9%–33.7%. It was found that the degradation rate of high-molecular-weight(HMW) PAHs(5-and 6-ring PAHs) was significantly(P < 0.05) higher than that of low-molecular-weight(LMW) PAHs(2–4-ring PAHs) regardless of the type of biochar used. Additionally, all three types of biochar significantly increased the relative abundance of the dominant bacterial phyla and genera in soil. Redundancy and correlation analyses also showed that there was a strong correlation between the removal rate of PAHs and dominant bacteria in the rhizosphere soil. This study indicated that biochar effectively reduced the health risk from dietary exposure to PAHs in wheat grains by increasing the abundance of bacteria related to PAH degradation, promoting the biodegradation of PAHs in the rhizosphere soil, and consequently reducing PAH uptake by wheat.

Fate of PM2.5-bound PAHs in Xiangyang, central China during 2018 Chinese spring festival: Influence of fireworks burning and air-mass transport

Variations of levels,possible source and air mass transmission were investigated for 16 USEPA priority-controlled PAHs in PM2.5 during 2018 Chinese Spring Festival(CSF)in Xiangyang City,central China which is the North-South pollutant airmass transport channel of China.Totally 37 samples were collected.Mass concentrations of 16 PAHs for the Pre–CSF day(Pre–CSFD),during the CSF day(CSFD)and after the CSF day(Af–CSFD)are 33.78±17.68 ng/m3,22.98±6.49 ng/m3,and 8.99±4.44 ng/m3,respectively.High resolution samples showed that 16 PAHs are higher in the morning(06:00–11:00)or afternoon(11:30–16:30),than those in the evening(17:00–22:00)and at night(22:30–05:30),whereas the result is reversed during the CSFD.Fireworks burning can obviously increase the mass concentration of PAHs.Air mass trajectory indicated that Xiangyang is a sink area of pollutants for northwest and southeast,and the sources of the northeast and southwest.The air mass only can be transmitted out through northeast and southwest.It is effective for improvement of air quality in Wuhan and Hunan to control fireworks emission in Henan and local areas.Fireworks burning was an important source for PAHs during CSFD,biomass,coal combustion,and traffic emission were the main sources of PAHs for Pre–CSFD and Af–CSFD periods.The health risk on the CSFD was higher than the acceptable levels,especially during the intensive fireworks burning,the risk value far exceed 1.0×10^-4,controlling burning fireworks is required.