| In recent years,the economy of the Pearl River Delta region has developed rapidly,and industry and intensive agriculture(vegetable fields)have developed rapidly,but the problem of environmental pollution has followed.Taking Foshan area as an example,non-point source and heavy metal pollution has always been a hot topic.The discharge of sewage from factories in Foshan area is large and unreasonable,the index of multiple cropping of vegetable fields in the suburbs is high,and some vegetable fields are matured three times a year or five crops in two years.in addition,there are some problems,such as excessive application of fertilizer and unreasonable single use.It is the main cause of non-point source pollution of heavy metals and nitrogen and phosphorus in vegetable fields in the suburbs of Foshan.However,in recent years,there has been a lack of investigation on the contents of nitrogen,phosphorus and potassium in vegetable fields and the contents of heavy metals in soil and vegetables in the suburbs of Foshan area.At the same time,the relationship between soil,vegetable heavy metal status and human health status in typical urban villages in this area is not clear.In this paper,the representative research area is selected to carry out the questionnaire work,and a total of 90 valid questionnaires are collected.At the same time,56 typical vegetable soil samples,28 agricultural irrigation water samples,116 vegetable samples and 103 human hair samples were collected in the study area.The contents of heavy metals such as alkali-hydrolyzed nitrogen,total nitrogen,available phosphorus,total phosphorus,available potassium and cadmium,copper,manganese,aluminum,selenium,mercury and arsenic were measured,and the present situation of nutrients and heavy metal contents in vegetable fields and vegetables in the suburbs of Foshan City was analyzed.On this basis,through the analysis of the basic characteristics of the sample and the use of pollution index method and other quality evaluation methods,the relationship between industrial structure(mainly industrial scale and size)and nitrogen and phosphorus non-point sources and heavy metal pollution in suburban vegetable fields in Foshan area was discussed.The potential relationship between the health of urban village residents(reflected by the content of heavy metals in human hair)and the content of heavy metals in vegetable soil /irrigation water and vegetables was also explored.The main results and conclusions of this study are as follows:(1)At present,Foshan industrial producing area is mainly concentrated in Nanhai District and Chancheng District,so the sampling frequency of vegetable soil in Nanhai and Chancheng areas is encrypted.The results of field visit and investigation showed that the order of potential industrial pollution in the vegetable planting areas of the five districts of Foshan was as follows: Sanshui,Chancheng < Gaoming <Nanhai.Within the jurisdiction of the same district,the potential pollution risk of vegetable land in different villages in different cities is significantly related to the industrial type,density and industrial development around the villages in the city.(2)The present situation of soil nitrogen,phosphorus and potassium content in vegetable fields in Foshan:(1)The average contents of alkali-hydrolyzed nitrogen and total phosphorus in vegetable soils in the suburbs of Foshan City were 151.9mg/kg and 1.97 g/kg,respectively.It is in the first level standard of nutrient classification in the second national soil census;The average contents of available phosphorus and available potassium were 24.7 mg/kg and 155.2 mg/kg,respectively,which were in the secondary standard,and the average content of total nitrogen was1.48 g/kg,which was the third grade standard.(2)The coefficient of variation from large to small was available phosphorus(105.7%),alkali-hydrolyzed nitrogen(62.6%),total nitrogen(41.9%),total phosphorus(39.1%)and available potassium(34.9%).(3)The nutrient contents of vegetable soils in different regions were significantly different,such as: total nitrogen from small to large for Nanhai,Gaoming,Chancheng,Sanshui,alkali-hydrolyzed nitrogen from large to small for Nanhai,Gaoming,Chancheng,Sanshui;Total phosphorus from large to small for the Nanhai,Gaoming,Sanshui,Chancheng;available phosphorus from large to small for Sanshui,Chancheng,Gaoming,Nanhai;available potassium from large to small for the Nanhai,Chancheng,Gaoming,Sanshui.Therefore,in view of the vegetable planting area in the suburbs of Foshan City,it is necessary to take better water and fertilizer management measures to control nitrogen and phosphorus according to the present situation of nutrient content and the fertilizer requirement characteristics of planting vegetables.In order to avoid the potential non-point source pollution risk in the vegetable planting area on the outskirts of Foshan.(3)The present situation of heavy metal content in vegetable soil,irrigation water and vegetables in the suburbs of Foshan:(1)The rate of cadmium,mercury and arsenic in soil exceeded the standard by 71.4%,8.6% and 0% respectively;The exceeding rate of cadmium in agricultural irrigation was 100%,and that of mercury and arsenic was 0.It can be seen that the pollution of cadmium in vegetable soil in the suburbs of Foshan is serious,while the pollution of mercury and arsenic is light,and copper and manganese should also be monitored in a timely manner.(2)The content of copper,manganese and selenium in soil was much higher than that in irrigation,while the average content of aluminum in irrigation was 2.58 mg/kg,which was higher than that in soil(0.47 mg/kg).(3)The exceeding rate of cadmium in vegetables from high to low was tuber vegetables(44.4%),leafy vegetables(43.7%)and legumes(25.0%),the exceeding rate of mercury from high to low was root and tuber vegetables(44.4%),leafy vegetables(33.6%)and legumes vegetables(25.0%).The rate of arsenic exceeding the standard was root and tuber vegetables(33.3%),leafy vegetables(12.6%)and legumes(0%)from high to low.It can be seen that there are some differences in the absorption and enrichment ability of 7 kinds of heavy metals in the three kinds of vegetables.the ability of root and tuber vegetables to absorb heavy metals is the strongest,and that of legumes is the weakest.(4)Based on the results of the questionnaire,five urban villages,such as Ditian Village and Luonan Village in Chancheng District with light pollution risk and Zengjia Village in Nanhai District,Haizhou Village in Nanhai District with medium pollution risk and Tan Bian Village with heavy pollution risk,were further investigated and analyzed.The results showed that the scale,type,water and fertilizer mode of vegetable field,the amount of self-grown vegetables and the diet structure of the residents in the village in the city had a comprehensive influence on the content of heavy metals in human hair.(1)The denser the industrial plant next to the vegetable field,the higher the content of heavy metals in human hair;(2)Sediment is often used as fertilizer.The higher the content of heavy metals in the hair of residents irrigated with river water;(3)The higher the content of heavy metals in the hair of residents who ate vegetables all the year round.It can be seen that the heavy metal elements in the environment can endanger the human health of the residents of the village in the city through the transmission chain of "industry-soil-agricultural irrigation water-vegetable". |
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