The Sorption-desorption And Degradation Of Organic Contaminants From Stormwater Road Runoff

Many organic contaminants are transported to aquatic environments via stormwater(e.g.,overland flow from residential,commercial,and industrial peri-urban areas)and roadway runoff.This runoff typically contains contaminants from diverse chemical classes such as pesticides,vehicle-derived chemicals,industrial and commercial chemicals,as well as pharmaceuticals and personal care products.Urban stormwater runoff degrades water quality,often affecting public health and aquatic ecosystems due to the toxicity risks of the pathogens,metals,and diverse organic contaminants comprising these complex mixtures.Because stormwater and roadway runoff typically enter receiving waters through intermittent and spatially diffuse flows,humans typically manage the risks to ecological and human health via“natural attenuation”.This natural attenuation approach,whether implicit or explicit,reflects the combined contributions of dilution,sequestration,and transformation mechanisms on observed contaminant concentrations.Thus investigating the sorption and degradation of these stormwater derived contaminants that has not been reported so far helps accessing the environmental risks.In this study,the sorption of 11 contaminants that has regularly been detected in stormwater were investigated using engineered model sorbent(40%compost and 60%soil),sorption and desorption of four novel contaminants(DPG,NMD,CPU,HMMM)were investigated in four soil and engineered model sorbent,we studied the influence of p H and figured out the sorption mechanism for each chemical.The sorption ability(log K_oc)showed anticorrelation with octanol-water partition coefficient(log D_ow).This indicated that hydrophobic interaction was not the only mechanism that contributed to the uptake of these contaminants.The sorption of two ionizable compounds(DPG,NMD)increased with increasing p H,this could be due to the increased ratio of neutral species with increasing p H.Sorption for two un-ionizable compounds(HMMM and CPU)generally remained unchanged with increasing p H.All compounds showed desorption hysteresis in all sorbents,and HI index increased with aqueous concentration.The hysteresis could be caused by 1)physical entrapment of contaminants by soil organic compounds(SOM);2)chemical bonding with SOM.HMMM concentration decreased with elapse with time,indicating it was hydrolyzed in water phase.This study explored the hydrolysis of HMMM at 3 different p H and 5 different temperature.Results showed that hydrolyzation ratio increased with decreasing p H and increasing temperature,the second order rate constant of H⁺catalyzed HMMM hydrolyzation at 20?,30?,40?,50?were calculated to be 3.67×10⁴,1.33×10⁵,4.85×10⁵and 1.25×10⁶M^-1d^-1 respectively.Arrhenius equation was utilized to calculate activation energy(Ea).22transformation products(TPs)were identified,the number of TPs increased with p H.12,14and 17 TPs were detected at p H 3.1,5.0 and 6.7 respectively,including chemicals that had been frequently detected with HMMM at various sampling sites,i.e.,PMMM,TMMM,HMPE.Melamine-one of the TPs that majorly generated at neutral p H were quantified using chemical standard.The yield of melamine at p H 6.7 was 4.05%,at p H 5.0 it was about 1/10 of that at p H 6.7,and no melamine was detected at p H 3.1.And melamine were hydrolytically stable at p H 6.7 at 50?,indicating that it could be the final hydrolyzation product of HMMM.Besides,the photocatalyzed degradation of three organophosphorus ester including Tris(2-chloroethyl)phosphate(TCEP),Tris(1-chloro-2-propyl)phosphate(TCPP)and Tris(1,3-dichloro-2-propyl)phosphate(TDCPP)were investigated.The Ti O₂ and UV light were used as catalysis,results showed that this significantly increased the OPEs degradation rate;inorganic ions(NO₃^-,Cl^-,SO₄^2-,PO₄^3-)would inhibit degradation of OPEs.·OH signal in different reaction systems were analyzed using ESR,results showed that·OH signal was prohibited by inorganic ions and fluic acid,thus resulting lower OPEs degradation efficiency.Inorder to simplify the calculation of degradation kinetics of OPEs under·OH and·SO₄^-treatment,p CBA was used as a probe compound,the simplified kinetic were successfully applied to calculate and predict the degradation of OPEs by·OH and·SO₄^-,the availability of the simplified model in natural water need further investigation.In conclusion,once these stormwater derived contaminants leached into surface water,some will be sorbed by natural soil,the ability and hysteresis of which depend on chemical properties(including solubility,speciation and specific moieties);some compounds like HMMM were not stable and would be hydrolyzed,thus generating multiple TPs.These TPs were also unstable in natural water yielding the final TP-melamine;compounds like OPEs can neither be hydrolyzed nor photodegraded,indicating that they were easy to transport in the environment and other effective measurements like photocatalysis should be taken.