The Experimental Study Of Accumulation And Toxicity About Lead In Rat Induced By Purified Water

With the improvement of people's living standard, consuming high-energy and refined food is common in the world. And the mineral matter in the food kept on decreasing. However, drinking soft water is prevailed in the world. And the hard effect due to low calcium of soft water is still debated. Some one supports the hypothesis that the purpose of drinking water is supplement water, because the mineral mainly came from diet. Other supports hypothesis that the mineral matter in water is more bioavailability to a higher content and soft water can accelerate the mineral water elimination from body and increase dietary intake of toxic metals, people may be sickness due to drinking purified water long period. The biological effect of soft water on rat is useful to guide drinking water.A research reported that appropriate hardness of water prevent the absorption of toxic metal in stomach significantly. Low calcium in water can increase the absorption of lead from water. And high calcium in water or food can decrease the absorption of toxic metal such as chromium from water. But up to now, there were no research about the absorption, accumulation, and toxicity of the lead induced by purified water. In order to gain a better understanding of the effect of the soft drinking water (especially with the lead in water), we study the effect of the purified water on rat with different content of lead in water.Methods:Animal model: 104 SPF male weaning SD rats were randomly divided into eight groups: group 1 fed tap water, group 2 fed purified water, group 3 fed tap water with lead 50 mg/L(lead acetate water-solution), group 4 fed purified water with Lead 50 mg/L, group 5 fed tap water with Lead 200 mg/L, group 6 fed purified water with Lead 200 mg/L, group 7 fed tap water with Lead 800 mg/L, and group 8 fed purified water with Lead 800 mg/L. All were fed with normal food and environmental cognitions kept consistent.Tap water: total dissolved solids(TDS) 175mg/L, conductivity 350μS/cm,chemical oxygen demand (COD) under detection,pb²⁺5.7μg/L. Purified drinking water:TDS 1.16mg/L,conductivity 2.28μS/cm,COD under detection, pb²⁺ under detection.Experimental examination index was thatâ‘ The animals were weighed weekly, the amount of diet and water consumed were recorded.â‘¡The level of blood lead were measured at 4,6,8,10,24,28 weeks of lead exposure.â‘¢Morris water maze(including Place Navigation, Spatial Probe Test, Visible Platform Trial)was measured at 12,24 week.â‘£The brain, heart, liver, kidney, bone were collected 28 weeks after lead exposure, and the lead concentrations were detected by graphite furnace atomic absorption spectrometric method.⑤The NR1, NR2A, NR2B of NMDAR (N-methyl-D-aspartame receptor) in hippocampus were analyzed by RT-PCR.â‘¥Zinc protoporphyrin levels were measured by surface fluorescence method.⑦PTH and OC in serum was measured by radioimmunoassay.⑧The level of calcium and magnesium in blood and bone were detected with atomic absorption spectrophotometer..⑨The level of MT in liver and kidney were measured by enzyme linked immunosorbent assay.The main results and conclusions are summarized as follows:Part one: The model of chronic lead accumulation and toxicity induced by purified water was establishedThe effect of the purified water was decrypted as follows:(1) The effect of purified water on the growth During the experiment, the body weight was increasing continuously, but there were no significant difference in the groups. The behavior and autonomic activities were normal.(2) The effect of purified water on the blood lead contentThe level of blood lead increased with lead concentration increase in drinking water and exposure time. And the level of blood lead in all lead treated group were more than 100μg/L(which is the children lead intoxication threshold of US CDC), especially the content in the high dosage group was more than 1000μg/L, and the lead severe intoxication threshold of US CDC is 450μg/L ⁷00μg/L. But no significant difference of blood lead level were noted between the rats drinking purified water and tap water at the same lead concentration treated group, such as group 1,2 and group 3,4.(3) The effect of purified water on the blood calcium and magnesium content No differences were noted for blood calcium and blood magnesium induced by purified water.(4) The effect of purified water on the zinc protoporphyrin levelThe level of zinc protoporphyrin increased with lead concentration increase in drinking water, and the Zinc protoporphyrin level in the dringking purified water group was higher than the drinking tap water group, such as group 2>group 1, group 4>group 3.In a word, the model of chronic lead accumulation and toxicity induced by purified water was established successfully.Part two: The lead accumulation in tissues of rat induced by long-term drinking purified waterThe effect of the purified water was decrypted as follows:(1) The effect of purified water on the lead content in tissueIn the same lead concentration treated groups, the lead level of the brain, heart, liver, kidney, and bone in the drinking purified water group was significantly higher than the drinking tap water group. For example, the lead in the heart, kidney were noted significantly difference in group 1, 2 and group 3, 4; the lead in the liver were noted significantly difference in the group 1, 2 and group 3, 4. It is notable that the lead in the kidney, liver, heart and brain in the purified water group were significantly difference in tap water group, such as group 2>group 1, group 4>group 3. It suggested drinking purified water long term can increase the lead accumulation in tissue.(2) The effect of purified water on the bone's calcium, magnesium and related hormoneThe serum parathyroid hormone increased and the osteocalcin decreased induced by lead exposure, and drinking purified water can accelerate theses change. There were no significant difference in the content of the serum calcium and serum magnesium, but the calcium content of the bone decreased with the lead content increase, and purified water can enhance this decrease. The change of magnesium in bone is similar. It indicated that purified water interfere the metabolism of calcium and magnesium.(3) The effect of purified water on the metallothioneins in liver and kidneyMetallothioneins are a group of low-molecular weight, cysteine rich intracellular proteins, which plays an important role in lead deintoxication. In our experiment, Metallothioneins increased with lead concentration increase in drinking water. Metallothioneins in the rats drinking purified water was higher than that of drinking tap water, such as group 2>group 1, group 4>group 3. This is consistent to the lead level of the liver. It suggested that the lead accumulation in liver increase by drinking purified water long period, more and more MT expressed in liver to attenuate the lead toxicity. The level of MT in the kidney deceased induced by purified water, because the high lead burden induced MT exhausted and the kidney could not synthesis MT.Part three: The effect of purified water on the spatial learning and memory abilityIn the 24 week Morris water maze, place navigation test's escape latency showed significantly prolonged at the rats drinking purified water compared with that drinking tap water on the pairs of 50 mg/L and 200 mg/L pb²⁺ groups(p<0.05), and the difference was occurred only in early 1² days. It suggested drinking purified water can aggravate the learning ability delay induced by lead.Expression of NR1,NR2A and NR2B in hippocampus of the rats drinking purified water was lower than that drinking tap water, especially at low lead exposure (50 mg/L, group 3>group 4) (p<0.05).Compared with drinking tap water, drinking purified water can increase the accumulation of brain lead, lower NR1,NR2A,NR2B expression and delay the spatial learning and memory ability under chronic lead exposure in water.Conclusion and prospect:In a word, drinking purified water long period can increase the lead accumulation in tissue, aggravate the toxicity on hematopoietic system; interfere the metabolism of bone calcium and magnesium, lower NR1, NR2A, NR2B expression and delay the spatial learning and memory ability, especially under chronic lead exposure in water. So drinking purified water should be carefully considered, especially for susceptible population.Due to limitation of time, our experiment is not perfect. For example, the expression of NMDAR, DMT1 should be studied by Western Blot. In order to gain a better understanding of the effect of the purified drinking water, we would study the metabolism change of poison or medicine induced by drinking purified water.