I. Geochemical samples of biological environment
The sampling design scheme is shown in Figure 2- 1. According to the incidence in this area, the sampling groups were divided into three groups: high incidence group (H), moderate incidence group (M), low incidence group or no incidence group (N). Each group selects 5 sampling villages, and each sampling village selects 5 sampling points. Five soil samples, five food samples, five human hair samples and 1 sample were collected by pairing (only 1 sample was selected in each sampling village, because the water in the village came from a unified well), and a small number of blood samples were collected in individual research areas.
Figure 2- 1 Schematic diagram of sampling design
(1) soil sample
Soil samples cover all kinds of soil types in each village as much as possible, and all topsoil is collected. Each sample was collected from the same cultivated land, and a square of about 20m×20m was arranged during collection. Take soil 10~20cm below the surface from four vertices with a sampling drill (Dutch soil drill), and discard topsoil above 10 ~ 20cm. Uniformly mix the soil at four points on the plastic sheet to remove stones, grass roots, etc. , divided into four parts, take two diagonal samples and put them in sample bags respectively. One of them was sent to the British Geological Survey for analysis, and the other was analyzed by the Testing Institute of the Academy of Geological Sciences. In addition, for every 10 soil sample collected, add a duplicate sample, drill duplicate samples at the four vertices of the same sample repeatedly, and bag them after the same treatment. In addition, in order to understand the change of selenium content in deep soil, some soil samples with depth over 30 ~ 45 cm were collected. Weight of each soil sample 100 ~ 200 g.
(2) Grain samples
When collecting food samples, the selection of varieties should represent the long-term eating habits of local residents as much as possible. Therefore, wheat and naked oats are selected as the main sampling objects in Zhangjiakou area, wheat and corn are mainly collected in Cixian research area and rice and corn are mainly collected in Enshi research area. For cultivated land without the above crops, the corresponding varieties of millet and other crops should be levied according to the actual situation. Most of the grain samples collected match the soil samples, but most of the samples in Enshi area cannot match the soil because the harvest season has passed. In the process of collection, human pollution should be avoided as much as possible, and crop seeds should be collected directly from the field. The sample weighs about 200 ~ 250 g, mixed evenly, put into two special white cloth sample bags, and keep it ventilated and dry to avoid mildew. A duplicate sample was collected every 20 samples.
After the grain samples are taken back to dry, they are knocked and ground on hardwood boards with wooden sticks or rubber hammers to remove chaff. After passing through the plastic screen, they are divided into two parts, which are put into paper bags and kept by the Institute of Testing of the Academy of Geological Sciences and the British Geological Survey.
(3) Water sample
In principle, each sampling village collects 1 water sample, and every five water samples increase 1 repeated sample. Samples are taken from wells, springs, water storage pits or reservoirs that villagers drink together.
The sampling tool includes a plastic syringe, a filter cartridge with a diameter of 25 mm and a 0.45 micron filter membrane at the front end, and two 50 ml polyethylene bottles. Before sampling, all kinds of tools need to use syringes to suck out the water at the sampling point and wash it twice to avoid cross-contamination. Collect 200ml of water from each sampling point. Filter 100ml, inject 100ml into two polyethylene bottles respectively, and seal. Before on-site sampling is completed, two deionized water samples are added as blank samples, at the same time, 330ml unfiltered water samples are added to each sampling point and put into plastic bottles, and the determination of pH, Eh, bicarbonate and conductivity is completed on site or on the same day.
(4) Human hair samples
According to the epidemic characteristics of diseases in different research areas, human hair samples are mainly collected from women of different ages in Zhangjiakou area; Cixian area mainly collects adults aged 20 ~ 60, and Enshi research area mainly includes children (Keshan endemic area) and adult men (poisoning area). Hair samples were taken from pillows, less than 5cm, and weighed about 2 ~ 5g g. After mixing evenly, divide them into two parts, put them into two sealed plastic bags respectively, and hand them over to the Testing Institute of the Academy of Geological Sciences and the British Geological Survey for preservation. Most of the hair samples do not match the soil and grain samples, but they are all controlled in the sampling village.
(5) Blood samples
Due to the difficulty in collection, only a small amount of human blood samples were collected in the sick villages in Zhangjiakou area. When collecting, take about 5ml of fasting venous blood, put it in a glass test tube and plug it tightly to prevent pollution and evaporation, and centrifuge it on the same day. Take 2 ~ 3ml of the upper transparent serum, put it into a sealed test tube with a plug, transport it back to Beijing for cold storage, and analyze it by the Institute of Geology.
Two. Geological and geochemical environment background samples
These samples were collected along a comprehensive geological and geochemical profile. It mainly includes rock samples, non-cultivated soil surface samples, depth profile samples and river sediment samples. There are two sections in Zhangjiakou, one starts from Maoyu, Chicheng County in the south, ends at Houpingtouliang, Guyuan County in the north, and runs northeast, with a length of 39.4km；; The other runs from the current map of chongli in the south to Lala Hsu in Zhangbei County in the north, with a total length of 35 kilometers. The two sections pass through Keshan village, which is seriously ill, moderately light and disease-free, and two different landscape areas, Bashang and Basha. The two sections designed by Cixian County respectively pass through the mountainous-hilly-plain landscape area and the high, medium and low incidence area of esophageal cancer. One from Fangguan in Shexian County-Beijiabi in Cixian County-Fengfeng Mining Area-Cixian Chengguan-Linzhang Chengguan-wei county Chengguan, with a total length of 90km；; The other section starts from Hezhang at the junction of Shexian and Cixian, passes through Guantai and Xibao, and reaches Wujiang Town, with a length of about 40km. When collecting samples, a soil sample and corresponding samples of rocks or river sediments (if there are exposed rocks or river sediments) are generally collected every 2 ~ 3 km. In Enshi research area, samples of regional geochemical water system sediments were collected, so no profile measurement was carried out, but various rock samples were collected in this area.
This project * * * collected 144 1 sample. See table 2- 1 for the number of samples of various types and study areas.
Table 2- 1 area sampling statistics of various studies