There is an obvious regional longevity phenomenon in China and many longevity counties are located in South China. This study was carried out to find the characteristics of elemental contents of drinking water in longevity areas in South China and the differences to non-longevity areas in China. A total of 128 drinking water samples were collected from longevity areas in South China (n = 40), non-longevity areas in South China (n = 74) and non-longevity areas in North China (n = 14) and 46 parameters of water were determined or calculated. The results showed that drinking water in longevity areas of South China had a high ratio of sum concentration of essential micro-elements in sum concentration of micro-elements (SCME) and a low ratio of sum concentration of hazardous micro-elements in SCME. The concentration of total hardness (TH) and strontium in drinking water was 157.82 mg/L and 82.1 μg/L, respectively, and they were 14.61 mg/L, 7.45 μg/L and 291.69 mg/L, 748.65 μg/L in the non-longevity areas of South and North China, respectively. The study concluded that drinking water containing 157.82 mg/L TH and 82.1 μg/L strontium in South China may be optimum to human health.

INTRODUCTION

Water is an important component of the human body, providing many essential macro- and micro-elements and playing an important role in human health (Nkono & Asubiojo 1997). Hamilton et al. (1973) found a similarity between the abundance of elements present in human tissues and average crystal rocks. Drinking water is also important for the environmental influences of human health (Nkono & Asubiojo 1997).

Increasing attention is being paid to the quality of drinking water worldwide. Water quality can be affected by the natural background and anthropogenic activities. Natural sources of elements are largely the result of chemical weathering of rock or volcanic activity, both of which can have considerable spatial variability (Ritter et al. 2002). In some rural areas in China, there is no official tap water and local residents usually drink water from mountain springs or river water. The quality of drinking water in these areas has a long-term impact on local residents’ health.

The chemical and physical properties of elements influence their availability for uptake by biological organisms and their potential to be toxic to organisms, as well as transport mechanisms in natural waters (Ritter et al. 2002). Drinking water contains various micro-elements, some of which have been widely implicated in human health and disease (Kumar et al. 2016). Elements such as fluorine (F), iron (Fe), manganese (Mn), copper (Cu), cobalt (Co), molybdenum (Mo), zinc (Zn), chromium (Cr), selenium (Se), nickel (Ni), vanadium (V), and silicon (Si) are essential for the growth of human and other living organisms. Even though some of the micro-elements are essential to man, at elevated levels both essential and non-essential elements can pose a hazardous risk to humans (WHO 1996). Elevated level of F in drinking water can result in problems of increased dental caries and of the development of bone deformities (Zhang et al. 2007), and long-term exposure to arsenic in drinking water at elevated levels can result in skin problems, kidney and lung cancers (Smith et al. 2002).

There is an obvious regional longevity phenomenon in China (Xin-min 2006). The distribution of centenarians in China is very uneven, and the longevity counties are geographically concentrated in South China. Bama, Donglan, Fengshan, Rugao, Chengmai, Lingao, and Sanshui are famous longevity counties in South China. The occurrences of centenarians (OC) (the number of centenarians per 100,000 inhabitants) in these counties are higher than the average level of China and most of the other counties in China. The elemental contents of drinking water in longevity counties in China have been studied by many researchers, but the study areas have always been limited to one longevity county. Until now, the characteristics of elemental contents of drinking water in longevity areas of South China and the difference to non-longevity areas in China have not been clear. Therefore, this study was carried out to investigate the elemental contents of drinking water in the longevity areas of South China and the differences compared to the non-longevity counties in China.

MATERIALS AND METHODS

Natural geographic setting

China is divided into South and North China by Kunlun-Qinling Mountain and the Huaihe River. In South China, the annual precipitation is higher than 800 mm, and the climate belongs to the subtropical monsoon generally. The annual precipitation in North China is lower than 800 mm and the climate belongs to the temperate continental monsoon generally. The study areas are located in South China, except for Huxian, Xinxiang, and Xilinhot counties which are located in North China. More details of the natural geography of those counties are shown in Table S1 (available with the online version of this paper).

Sample collection

A field survey was conducted to collect the drinking water samples from longevity and non-longevity counties of South China. For comparative analysis the drinking water was also collected from the non-longevity counties of North China. First, the percentage of centenarian to county levels was calculated from the national population census (NBS 2010). A total of 128 samples (Table 1) was collected that included 86% of groundwater (spring water and well water) and 14% of surface water (lake water, river water, and reservoir water). Samples collected from longevity areas accounted for 31% and the other 69% was collected from non-longevity areas.

Table 1

Number of samples in the study areas

  Province County Lake water Reservoir water River water Spring water Well water Total 
North Henan Xinxiang     
Inner Mongolia Xilinhot     
Shaanxi Huxian     
South Guangdong Guangning    31  31 
 Huaiji   12 18 
 Sihui   10 
 Sanshui*    
Guangxi Bama*    
 Donglan*   13 
 Fengshan*   
 Heshan     
 Nanning     
 Tianyang     
Hainan Chengmai*     
 Lingao*     
 Sanya   
Jiangsu Rugao*   
 Suzhou    
Total   62 48 128 
  Province County Lake water Reservoir water River water Spring water Well water Total 
North Henan Xinxiang     
Inner Mongolia Xilinhot     
Shaanxi Huxian     
South Guangdong Guangning    31  31 
 Huaiji   12 18 
 Sihui   10 
 Sanshui*    
Guangxi Bama*    
 Donglan*   13 
 Fengshan*   
 Heshan     
 Nanning     
 Tianyang     
Hainan Chengmai*     
 Lingao*     
 Sanya   
Jiangsu Rugao*   
 Suzhou    
Total   62 48 128 

*Represents longevity counties.

Samples were collected from the households of local inhabitants or from potable water sources (Figure 1). All the samples were collected far away from industrial and mining enterprises and the water sources had not changed for many years. No water pollution had been found according to the local inhabitants and previous literature.
Figure 1

Distribution of longevity counties in China and sample spots.

Figure 1

Distribution of longevity counties in China and sample spots.

The samples were collected in colorless polythene plastic bottles that had been washed once with distilled water and three times with sample water; this way the chances of contamination in the sample collection would be small. All water samples were stored in clean plastic bottles at 4 °C before further analysis. Details of the sampling method can be found in Methods for Chemical Analysis of Water and Waste Water (MEPPRC 2002).

Analytical methods

The concentrations of Ca, Mg, Na, K, SO2−4, SiO2, B, P, Sr were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) (PerkinElmer, Optima 5300 DV) and elements Al, Ba, Be, Cd, Co, Cr, Cu, Li, Mn, Ni, Pb, Tl, V, Cs, Ga, In, Rb, U, Bi, Mo, Zn, and Fe were tested by ICP-mass spectrometry (ICP-MS) (PerkinElmer, Elan DRC-e). The pH, electrical conductivity (EC), and oxidation–reduction potential (Eh) were determined in situ using a SevenGo SG2/3 analyzer (Mettler Toledo Company, Shanghai, China). Bicarbonate (HCO3) was determined using an acid–base titration method within 3 days of sampling. Nitrate (NO3) and chlorine (Cl) concentrations in water were determined by ion chromatography (Dionex Inc., Dionex-ICS-900). Total dissolved solids (TDS) were equal to the sum of ions except bicarbonate (HCO3) and half of HCO3. Total hardness (TH) was calculated by the concentration of Ca and Mg.

For determining selenium (Se), 10 mL samples and 5 mL concentrated hydrochloric acid were added into 20 mL glass test tubes and heated in a boiling water bath for 40 minutes. For determining arsenic (As), 10 mL samples, 1 mL concentrated hydrochloric acid, and 1 mL reducing agent (2.5% thiourea + 2.5% ascorbic acid) were added, and allowed to stand for 40 minutes. Both Se and As were determined by hydride generation atomic fluorescence spectrometry (HG-AFS; Beijing Haiguang Instruments Co. Ltd).

The concentrations of elements were calculated by a five-point calibration curve with linearity of all target elements higher than 0.999. The precision of analyses was tested at regular intervals by running duplicate analyses of selected samples and internal standards. The precision and reproducibility were found to be within the confidence limit of 98%. The detection limit of ICP-MS was <0.1 μg/L and that of ICP-OES and ion chromatography <0.1 mg/L. The detection limit for As and Se was <0.01 μg/L. All the samples were determined in the Geochemistry Laboratory of the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences.

Statistical analysis

The Mann–Whitney U nonparametric test was applied as a hypothetical test because the distribution of data did not follow normal distribution or logarithmic distribution. Statistical Package of Social Science version 20 and Excel 2010 were used for the statistical analysis.

RESULTS

Longevity situation of the study areas

The OC (the number of centenarians per 100,000 inhabitants) is an important indicator of the longevity (Magnolfi et al. 2007; Stefanadis 2010; Willcox et al. 2010). However, OC was stongly affected by migration and birth rate (Magnolfi et al. 2007; Liu et al. 2014). To maintain OC, four new indices, namely, LI% (ratio of ultranonagenarians to those above 65 years old), CI% (ratio of centenarians within the ultranonagenarians), UOI% (ratio of people above 80 years old), UC (number of centenarians per 10,000 over 65 year-old subjects) were applied.

The longevity indices of OC, CI%, and UC in Guangxi province and Hainan province are significantly higher than those of other counties of China (Table 2). Bama and Lingao are typical longevity counties of China as almost all their indices are relatively higher. The differences of longevity indices are apparent and all five longevity indices of South China are all higher than those of North China. A thought-provoking phenomenon is that OC, CI%, and UC increase consecutively from north-west to south-east in the order of Huaiji, Guangning, Sihui, and Sanshui respectively. The OC, CI% and UC in Sanshui are 12.1-fold, 9-fold, and 14.2-fold, respectively, as compared to northern Huaiji.

Table 2

Longevity indices of study counties in China

Province County and city OC LI% CI % UOI% UC 
Guangdong Huaiji 0.74 2.27 0.4 1.46 0.92 
Guangning 2.59 1.89 1.24 2.18 2.34 
Sihui 5.16 3.06 2.09 1.86 6.38 
Sanshui 8.99 3.62 3.59 1.68 13.03 
Guangxi Fengshan 28.49 3.41 8.41 1.7 28.71 
Donglan 31.45 4.1 6.33 25.95 
Bama 35.61 4.24 9.32 1.65 39.54 
Nanning 1.54 2.13 1.07 1.14 2.27 
Heshan 5.24 2.82 2.09 1.68 5.89 
Tianyang 4.15 2.06 1.72 4.1 
Jiangsu Suzhou 1.5 1.99 0.97 1.61 1.93 
Rugao 8.21 2.35 2.08 3.61 4.89 
Hainan Chengmai 31.04 3.68 8.51 2.31 31.32 
Lingao 36.93 4.52 9.5 2.09 42.96 
Sanya 3.21 2.13 3.21 0.75 6.83 
Shaanxi Huxian 1.03 1.15 
Henan Xinxiang 0.88 1.92 0.62 1.44 1.2 
Inner Mongolia Xilinhot 0.58 1.19 0.58 1.2 0.69 
South China 3.01 1.80 1.82 1.68 3.28 
North China 2.24 1.47 1.77 1.42 2.61 
China 2.67 1.66 1.8 1.57 3.0 
Province County and city OC LI% CI % UOI% UC 
Guangdong Huaiji 0.74 2.27 0.4 1.46 0.92 
Guangning 2.59 1.89 1.24 2.18 2.34 
Sihui 5.16 3.06 2.09 1.86 6.38 
Sanshui 8.99 3.62 3.59 1.68 13.03 
Guangxi Fengshan 28.49 3.41 8.41 1.7 28.71 
Donglan 31.45 4.1 6.33 25.95 
Bama 35.61 4.24 9.32 1.65 39.54 
Nanning 1.54 2.13 1.07 1.14 2.27 
Heshan 5.24 2.82 2.09 1.68 5.89 
Tianyang 4.15 2.06 1.72 4.1 
Jiangsu Suzhou 1.5 1.99 0.97 1.61 1.93 
Rugao 8.21 2.35 2.08 3.61 4.89 
Hainan Chengmai 31.04 3.68 8.51 2.31 31.32 
Lingao 36.93 4.52 9.5 2.09 42.96 
Sanya 3.21 2.13 3.21 0.75 6.83 
Shaanxi Huxian 1.03 1.15 
Henan Xinxiang 0.88 1.92 0.62 1.44 1.2 
Inner Mongolia Xilinhot 0.58 1.19 0.58 1.2 0.69 
South China 3.01 1.80 1.82 1.68 3.28 
North China 2.24 1.47 1.77 1.42 2.61 
China 2.67 1.66 1.8 1.57 3.0 

OC: number of centenarians per 100,000 inhabitants; LI: ratio of ultranonagenarians to those above 65 years old; CI: ratio of centenarians within the ultranonagenarians; UOI: percentage of people above 80 years old; UC: number of centenarians per 10,000 over 65-year-old subjects.

Physico-chemical parameters of drinking water

Table 3 shows regular parameters and macro-elements of drinking water in longevity areas and non-longevity areas in South China as well as non-longevity areas in North China.

Table 3

Statistical summary of physico-chemical parameters in drinking waters of China

  Longevity in South n = 40
 
Non-longevity in South n = 74
 
Non-longevity in North n = 14
 
  
Elements Range Median Range Median Range Median GB 5749-2006 (MHPRC 2006WHO (WHO 2011
pH 6.62 ∼ 8.01 7.42 5.17 ∼ 9.18 7.07 7.42 ∼ 8.38 7.71 6.5–8.5 6.5–9.5 
EC 37.1 ∼ 1,536 329 10.33 ∼ 1,146 40.6 286 ∼ 2,430 699.50   
Eh 195 ∼ 337 231 120 ∼ 355 252 193 ∼ 290 225   
TDS 35.43 ∼ 1,014.66 209.02 18.41 ∼ 719.28 47.97 172.16 ∼ 1,725.65 441.44 1,000 1,000 
TH 20.14 ∼ 595.13 157.82 0.63 ∼ 471.15 14.61 59.2 ∼ 755.81 291.69 450 500 
HCO3 28.3 ∼ 737.74 189.67 3.58 ∼ 459.97 21.57 151.75 ∼ 662.96 337.48   
Ca 6.44 ∼ 138.1 50.84 0.17 ∼ 125.8 2.63 21.31 ∼ 120.5 49.56   
0.05 ∼ 62.52 1.31 0.13 ∼ 17.78 1.45 0.31 ∼ 8.35 1.28   
Mg 0.95 ∼ 71.89 2.89 0.05 ∼ 38.15 1.77 1.46 ∼ 128.1 31.02   
Na 0.28 ∼ 122.3 4.56 0.35 ∼ 76.4 2.95 28.67 ∼ 241.3 51.63 200 200 
SiO2 2.64 ∼ 48.17 9.89 2.02 ∼ 34.55 17.70 16.35 ∼ 28.49 19.26   
Cl 0.84 ∼ 148.57 3.26 0.16 ∼ 112.91 1.86 <0.1 ∼ 401.06 35.73 250 250 
SO2−4 0.2 ∼ 124.9 7.43 <0.1 ∼ 102.9 1.70 5.23 ∼ 639.9 35.44 250 500 
NO3 <0.1 ∼ 121.93 5.15 <0.1 ∼ 90.28 1.56 0.13 ∼ 51.59 0.57 44.3 50 
  Longevity in South n = 40
 
Non-longevity in South n = 74
 
Non-longevity in North n = 14
 
  
Elements Range Median Range Median Range Median GB 5749-2006 (MHPRC 2006WHO (WHO 2011
pH 6.62 ∼ 8.01 7.42 5.17 ∼ 9.18 7.07 7.42 ∼ 8.38 7.71 6.5–8.5 6.5–9.5 
EC 37.1 ∼ 1,536 329 10.33 ∼ 1,146 40.6 286 ∼ 2,430 699.50   
Eh 195 ∼ 337 231 120 ∼ 355 252 193 ∼ 290 225   
TDS 35.43 ∼ 1,014.66 209.02 18.41 ∼ 719.28 47.97 172.16 ∼ 1,725.65 441.44 1,000 1,000 
TH 20.14 ∼ 595.13 157.82 0.63 ∼ 471.15 14.61 59.2 ∼ 755.81 291.69 450 500 
HCO3 28.3 ∼ 737.74 189.67 3.58 ∼ 459.97 21.57 151.75 ∼ 662.96 337.48   
Ca 6.44 ∼ 138.1 50.84 0.17 ∼ 125.8 2.63 21.31 ∼ 120.5 49.56   
0.05 ∼ 62.52 1.31 0.13 ∼ 17.78 1.45 0.31 ∼ 8.35 1.28   
Mg 0.95 ∼ 71.89 2.89 0.05 ∼ 38.15 1.77 1.46 ∼ 128.1 31.02   
Na 0.28 ∼ 122.3 4.56 0.35 ∼ 76.4 2.95 28.67 ∼ 241.3 51.63 200 200 
SiO2 2.64 ∼ 48.17 9.89 2.02 ∼ 34.55 17.70 16.35 ∼ 28.49 19.26   
Cl 0.84 ∼ 148.57 3.26 0.16 ∼ 112.91 1.86 <0.1 ∼ 401.06 35.73 250 250 
SO2−4 0.2 ∼ 124.9 7.43 <0.1 ∼ 102.9 1.70 5.23 ∼ 639.9 35.44 250 500 
NO3 <0.1 ∼ 121.93 5.15 <0.1 ∼ 90.28 1.56 0.13 ∼ 51.59 0.57 44.3 50 

Unit: mg/L except EC (μS/cm) and Eh (mv).

n: number of samples.

TDS: total dissolved solids; TH: total hardness.

The pH value of drinking water in longevity areas of South China are 6.62 ∼ 8.01 with a median of 7.42, indicating drinking water in longevity areas of South China are slightly alkaline. The TDS of drinking water in longevity areas in South China ranges between 35.43 and 1,014.66 mg/L, varying from fresh water (TDS < 1,000 mg/L) to brackish water (1,000 < TDS <2,000 mg/L). The TH of drinking water is 20.14 ∼ 594.13 mg/L, varying from soft water (TH < 75 mg/L) to high-grade hard water (TH > 450 mg/L). The order of relative abundance of major cations of drinking water in longevity areas of South China is Ca > Na > Mg > K (on a mg/L basis), while that of anions is HCO3 > SO2−4 > NO3 > Cl. The concentration of micro-elements varies greatly (Table 4). The sum concentration of micro-elements (SCME) is 138.26 ∼ 2,269.66 μg/L with a median of 358.28 μg/L, and the top three micro-elements in decreasing order according to median value are Fe (108.66 μg/L) > Sr (82.1 μg/L) > Zn (7.97 μg/L). The ranges of the sum concentration of essential micro-elements (SCEE: Fe, Zn, Cu, Mn, Cr, Mo, Co, Ni, V, Se) and sum concentration of hazardous elements (SCHE: As, Cd, Pb) are more than one magnitude with a median of 160.17 μg/L and 1.26 μg/L, respectively. The ranges of the ratio of SCEE in SCME (SCEESCME) and the ratio of SCHE in SCME (SCHESCME) are within two magnitudes with a median of 0.4 and 0.035, respectively.

Table 4

Statistical summary of micro-elements in drinking waters of China

  Longevity in South n = 40
 
Non-longevity in South n = 74
 
Non-longevity in North n = 14
 
GB 5749-2006  
Elements Range Median Range Median Range Median (MHPRC 2006WHO (WHO 2011
Se <0.01 ∼ 7.29 0.12 0.02 ∼ 2.28 0.47 <0.01 ∼ 9.07 0.25 10 10 
As 0.12 ∼ 56.33 1.09 0.05 ∼ 7.46 0.72 0.92 ∼ 40.6 16.95 10 10 
Al <0.1 ∼ 109.02 6.04 0.86 ∼ 1,127.24 26.99 1.44 ∼ 52.17 5.8 200 200 
<0.1 ∼ 209.4 4.9 <0.1 ∼ 80.7 <0.1 15.4 ∼ 222.2 90.75 500 500 
Ba 1.75 ∼ 56.98 6.62 0.63 ∼ 195.04 22.71 19.99 ∼ 359.69 52 700  
Be <0.1 ∼ 0.07 <0.1 <0.1 ∼ 1.35 <0.1 <0.1 ∼ 0.28 0.01  
Cd <0.1 ∼ 1.66 0.02 <0.1 ∼ 0.51 0.02 0.01 ∼ 0.13 0.04 
Co 0.01 ∼ 0.56 0.07 <0.1 ∼ 18.24 0.03 0.03 ∼ 0.63 0.07   
Cr <0.1 ∼ 50.71 5.93 0.4 ∼ 39.22 3.27 3.49 ∼ 17.42 9.65 50 50 
Cu <0.1 ∼ 4.25 0.19 <0.1 ∼ 7.47 <0.1 0.28 ∼ 4.34 0.74 1,000 1,000 
Li <0.1 ∼ 36.71 0.82 0.05 ∼ 9.55 1.21 2.09 ∼ 37.22 13.49   
Mn <0.1 ∼ 34.92 0.79 <0.1 ∼ 1,213.4 1.01 0.05 ∼ 76.66 1.74 100 400 
Ni <0.1 ∼ 3.53 0.53 <0.1 ∼ 12.9 <0.1 <0.1 ∼ 2.76 0.64 20 70 
<0.1 ∼ 227.1 23.3 <0.1 ∼ 851.6 <0.1 8.7 ∼ 265.8 37.5   
Pb <0.1 ∼ 0.73 0.04 <0.1 ∼ 5.03 0.05 <0.1 ∼ 0.17 0.01 10 10 
Tl <0.1 ∼ 0.2 <0.1 ∼ 0.18 0.01 <0.1 ∼ 0 <0.1 0.1  
<0.1 ∼ 7.27 0.15 <0.1 ∼ 35.91 <0.1 0.45 ∼ 43.08 25.66   
Cs <0.1 ∼ 0.85 0.02 0 ∼ 0.81 0.06 0 ∼ 0.02 0.01   
Ga <0.1 ∼ 4.45 0.26 0.13 ∼ 12.36 1.28 0.49 ∼ 8.36 1.73   
In <0.1 ∼ 0 <0.1 <0.1 ∼ 0.01 <0.1 <0.1 ∼ 0.01 <0.1   
Rb <0.1 ∼ 78.88 1.26 0.55 ∼ 43.35 3.37 0.09 ∼ 1.29 0.39   
<0.1 ∼ 3.54 0.17 0 ∼ 9.84 0.03 0.12 ∼ 15.8 0.62  15 
Bi <0.1 ∼ 0.01 <0.1 ∼ 0.07 <0.1 ∼ 0.01   
Sr 20.3 ∼ 621.2 82.1 <0.1 ∼ 607.3 7.45 177 ∼ 2,005 748.65   
Mo <0.1 ∼ 5.1 0.15 <0.1 ∼ 5.85 0.07 0.93 ∼ 7.6 5.69 70 70 
Zn 1.08 ∼ 1,951.63 7.97 <0.1 ∼ 517.29 13.89 0.33 ∼ 197.49 11.99 1,000 3,000 
Fe <0.1 ∼ 278.78 108.66 <0.1 ∼ 214.85 42.04 33.63 ∼ 423.76 80.1 300 3,000 
SCME 138.26 ∼ 2,269.66 358.28 36.58 ∼ 2,691.33 204.53 592.78 ∼ 3,205.63 1,171.79   
SCEE 29.73 ∼ 2,209.73 160.17 9.13 ∼ 13,84.48 75.16 60.51 ∼ 550.99 158.65   
SCHE 0.2 ∼ 56.35 1.26 0.07 ∼ 7.54 0.96 1.13 ∼ 40.7 17.12   
SCEESCME 0.03 ∼ 0.98 0.40 0.04 ∼ 0.8 0.35 0.07 ∼ 0.23 0.14   
SCHESCME 0.0007 ∼ 0.053 0.0035 0.0002 ∼ 0.027 0.004 0.0004 ∼ 0.058 0.0107   
  Longevity in South n = 40
 
Non-longevity in South n = 74
 
Non-longevity in North n = 14
 
GB 5749-2006  
Elements Range Median Range Median Range Median (MHPRC 2006WHO (WHO 2011
Se <0.01 ∼ 7.29 0.12 0.02 ∼ 2.28 0.47 <0.01 ∼ 9.07 0.25 10 10 
As 0.12 ∼ 56.33 1.09 0.05 ∼ 7.46 0.72 0.92 ∼ 40.6 16.95 10 10 
Al <0.1 ∼ 109.02 6.04 0.86 ∼ 1,127.24 26.99 1.44 ∼ 52.17 5.8 200 200 
<0.1 ∼ 209.4 4.9 <0.1 ∼ 80.7 <0.1 15.4 ∼ 222.2 90.75 500 500 
Ba 1.75 ∼ 56.98 6.62 0.63 ∼ 195.04 22.71 19.99 ∼ 359.69 52 700  
Be <0.1 ∼ 0.07 <0.1 <0.1 ∼ 1.35 <0.1 <0.1 ∼ 0.28 0.01  
Cd <0.1 ∼ 1.66 0.02 <0.1 ∼ 0.51 0.02 0.01 ∼ 0.13 0.04 
Co 0.01 ∼ 0.56 0.07 <0.1 ∼ 18.24 0.03 0.03 ∼ 0.63 0.07   
Cr <0.1 ∼ 50.71 5.93 0.4 ∼ 39.22 3.27 3.49 ∼ 17.42 9.65 50 50 
Cu <0.1 ∼ 4.25 0.19 <0.1 ∼ 7.47 <0.1 0.28 ∼ 4.34 0.74 1,000 1,000 
Li <0.1 ∼ 36.71 0.82 0.05 ∼ 9.55 1.21 2.09 ∼ 37.22 13.49   
Mn <0.1 ∼ 34.92 0.79 <0.1 ∼ 1,213.4 1.01 0.05 ∼ 76.66 1.74 100 400 
Ni <0.1 ∼ 3.53 0.53 <0.1 ∼ 12.9 <0.1 <0.1 ∼ 2.76 0.64 20 70 
<0.1 ∼ 227.1 23.3 <0.1 ∼ 851.6 <0.1 8.7 ∼ 265.8 37.5   
Pb <0.1 ∼ 0.73 0.04 <0.1 ∼ 5.03 0.05 <0.1 ∼ 0.17 0.01 10 10 
Tl <0.1 ∼ 0.2 <0.1 ∼ 0.18 0.01 <0.1 ∼ 0 <0.1 0.1  
<0.1 ∼ 7.27 0.15 <0.1 ∼ 35.91 <0.1 0.45 ∼ 43.08 25.66   
Cs <0.1 ∼ 0.85 0.02 0 ∼ 0.81 0.06 0 ∼ 0.02 0.01   
Ga <0.1 ∼ 4.45 0.26 0.13 ∼ 12.36 1.28 0.49 ∼ 8.36 1.73   
In <0.1 ∼ 0 <0.1 <0.1 ∼ 0.01 <0.1 <0.1 ∼ 0.01 <0.1   
Rb <0.1 ∼ 78.88 1.26 0.55 ∼ 43.35 3.37 0.09 ∼ 1.29 0.39   
<0.1 ∼ 3.54 0.17 0 ∼ 9.84 0.03 0.12 ∼ 15.8 0.62  15 
Bi <0.1 ∼ 0.01 <0.1 ∼ 0.07 <0.1 ∼ 0.01   
Sr 20.3 ∼ 621.2 82.1 <0.1 ∼ 607.3 7.45 177 ∼ 2,005 748.65   
Mo <0.1 ∼ 5.1 0.15 <0.1 ∼ 5.85 0.07 0.93 ∼ 7.6 5.69 70 70 
Zn 1.08 ∼ 1,951.63 7.97 <0.1 ∼ 517.29 13.89 0.33 ∼ 197.49 11.99 1,000 3,000 
Fe <0.1 ∼ 278.78 108.66 <0.1 ∼ 214.85 42.04 33.63 ∼ 423.76 80.1 300 3,000 
SCME 138.26 ∼ 2,269.66 358.28 36.58 ∼ 2,691.33 204.53 592.78 ∼ 3,205.63 1,171.79   
SCEE 29.73 ∼ 2,209.73 160.17 9.13 ∼ 13,84.48 75.16 60.51 ∼ 550.99 158.65   
SCHE 0.2 ∼ 56.35 1.26 0.07 ∼ 7.54 0.96 1.13 ∼ 40.7 17.12   
SCEESCME 0.03 ∼ 0.98 0.40 0.04 ∼ 0.8 0.35 0.07 ∼ 0.23 0.14   
SCHESCME 0.0007 ∼ 0.053 0.0035 0.0002 ∼ 0.027 0.004 0.0004 ∼ 0.058 0.0107   

Unit: μg/L, except SCEESCME and SCHESCME.

∼: approximate.

n: number of samples.

SCME: sum concentration of micro-elements; SCEE: sum concentration of essential micro-elements (Fe, Zn, Cu, Mn, Cr, Mo, Co, Ni, V, Se); SCHE: sum concentration of hazardous elements (As, Cd, Pb); SCEESCME: ratio of SCEE in SCME; SCHESCME: ratio of SCHE in SCME.

The pH value of drinking water in non-longevity areas in South China is 5.17 ∼ 9.18 with a median of 7.07, indicating drinking water in non-longevity areas in South China is slightly alkaline or weakly acidic. The samples of drinking water in non-longevity areas in South China are all fresh water with TDS ranges between 18.41 and 719.28 mg/L. The TH of drinking water is 0.63 ∼ 471.15 mg/L, varying from over two orders of magnitude from soft water to hard water. The order of relative abundance of major cations of drinking water in non-longevity areas in South China is Na > Ca > Mg > K (mg/L), while that of anions is HCO3 > Cl > SO2−4 > NO3. The ranges of SCME, SCEE, SCHE, SCHESCME are no less than two magnitudes with a median of 204.53 μg/L, 75.16 μg/L, 0.96 μg/L, 0.004, respectively. The ranges of SCEESCME are within one magnitude with a median of 0.35. The top three micro-elements in decreasing order according to median value are Fe (42.04 μg/L) > Al (26.99 μg/L) > Ba (22.71 μg/L).

The pH value of drinking water in non-longevity areas in North China is 7.42 ∼ 8.38 with a median of 7.71, indicating drinking water in longevity areas in North China is slightly alkaline. The TDS of drinking water in longevity areas in North China ranges between 172.16 and 1,725.65 mg/L, varying from fresh water to brackish water. The TH of drinking water is 59.2 ∼ 755.81 mg/L, varying from over two orders of magnitude from soft water to high-grade hard water. The order of relative abundance of major cations of drinking water in non-longevity areas in North China is Na > Ca > Mg > K (mg/L), while that of anions is HCO3 > Cl > SO2−4>NO3. The concentration of micro-elements varies greatly. The ranges of SCME, SCEE, SCHE, SCEESCME are within one magnitude with medians of 1,171.79 μg/L, 158.65 μg/L, 17.12 μg/L, 0.14, respectively. The range of SCHESCME is within one magnitude with a median of 0.01 and the top three micro-elements in decreasing order according to median value are Sr (748.65 μg/L) > B (90.75 μ/L) > Fe (80.1 μg/L).

Drinking water quality

The quality of drinking water was evaluated based on recommended standards of the World Health Organization (WHO 2011) and National Standards for Drinking Water Quality of the People's Republic of China (MHPRC 2006).

In the longevity areas of South China, TDS, TH, As, Cr, Tl, Zn, and NO3 are 2.5%, 7.5%, 7.5%, 2.5%, 2.5%, 5%, and 7.5%, respectively, higher than the highest limits set by the National Standards for Drinking Water Quality of the People's Republic of China (MHPRC 2006), while their highest values are 1.01-fold, 1.32-fold, 5.63-fold, 1.01-fold, 1.98-fold, 1.95-fold, and 2.75-fold, respectively, as compared with the National Standards for Drinking Water Quality of the People's Republic of China (Tables 3 and 4).

In non-longevity areas of South China, TH, As, Mn, Tl, and NO3 are 1.35%, 12.16%, 4.05%, 6.76%, and 11.63%, respectively. These parameters in drinking water samples were higher than the highest limits of the standards set by the National Standards for Drinking Water Quality of the People's Republic of China (MHPRC 2006), while their highest values are 1.05-fold, 5.64-fold, 12.13-fold, 1.77-fold, and 3.86-fold respectively, as compared with the National Standards for Drinking Water Quality of the People's Republic of China. The pH in 20.27% of drinking water in non-longevity areas in South China is lower than the lowest limit of 6.5, and the highest and lowest values are 1.08-fold and 0.88-fold, respectively, by comparison with the highest limit (pH = 8.5) and lowest limit (pH = 6.5).

In non-longevity areas of North China, TDS, TH, As, Fe, Na, SO2−4, Cl and NO3 are 14.29%, 28.57%, 78.57%, 7.14%, 14.29%, 14.29%, 14.29%, and 11.11% of drinking water samples are higher than the respective limits set by the National Standards for Drinking Water Quality of the People's Republic of China (MHPRC 2006) and their highest values are 1.73-fold, 1.68-fold, 4.06-fold, 1.41-fold, 1.21-fold, 2.56-fold, 1.6-fold, and 1.16-fold, respectively, when compared with the National Standards for Drinking Water Quality of the People's Republic of China.

DISCUSSION

Variations between longevity and non-longevity areas’ drinking water quality

The parameters of drinking water from longevity areas and non-longevity areas in South China varied greatly. Mann–Whitney U nonparametric test was applied and the results showed significant difference (p < 0.05) in pH (1.05-fold, median value of longevity areas in South China was 1.05-fold that of non-longevity areas in South China; p = 0.011), EC (8.1-fold, p < 0.001), major iron HCO3 (8.79-fold, p < 0.001), Ca (19.36-fold, p < 0.001), Mg (1.63-fold, p < 0.001), SiO2 (0.56-fold, p = 0.014), SO2−4 (4.38-fold, p < 0.001), Cl (1.75-fold, p = 0.005), NO3 (3.31-fold, p = 0.028), and micro-elements Se (0.25-fold, p < 0.001), As (1.58-fold, p = 0.018), Al (0.22-fold, p = 0.002), B (BD, median value of longevity areas in South China was below detection, p < 0.001), Ba (0.29-fold, p < 0.001), Co (2.88-fold, p < 0.001), Cu (BD, p < 0.001), Ni (BD, p = 0.002), P (BD, p < 0.001), Tl (0.29-fold, p = 0.004), V (BD, p < 0.001), Cs (0.25-fold, p < 0.001), Ga (0.21-fold, p < 0.001), Rb (0.37-fold, p = 0.003), U (6.55-fold, p = 0.006), Sr (11.02-fold, p < 0.001), Fe (2.58-fold, p < 0.001), SCME (1.75-fold, p < 0.001) and SCEE (2.13-fold, p < 0.001).

Mann–Whitney U nonparametric test was applied on parameters of drinking water from longevity areas in South China versus non-longevity counties in North China, and the results showed significant difference (p < 0.05) in pH (0.96-fold, median value of longevity areas in South China was 0.96-fold that of non-longevity areas in North China, p < 0.001), EC (0.47-fold, p = 0.004), HCO3 (0.56-fold, p = 0.018), Mg (0.09-fold, p = 0.006), Na (0.09-fold, p < 0.001), SiO2 (0.51-fold, p = 0.003), SO2−4 (0.21-fold, p = 0.009), NO3 (9.03-fold, p = 0.022), Se (0.36-fold, p = 0.003), As (0.06-fold, p < 0.001), B (0.05-fold, p < 0.001), Ba (0.13-fold, p < 0.001), Be (0-fold, p = 0.026), Cd (0.52-fold, p = 0.034), Cu (0.26-fold, p = 0.009), Li (0.06-fold, p = 0.001), P (0.62-fold, p = 0.007), Pb (3.7-fold, p = 0.012), Tl (BD, median value of non-longevity areas in North China was below detection, p = 0.043), V (0.01-fold, p < 0.001), Cs (1.72-fold, p = 0.014), Ga (0.15-fold, p < 0.001), Rb (3.22-fold, p = 0.001), U (0.27-fold, p < 0.001), Sr (0.11-fold, p < 0.001), Mo (0.03-fold, p < 0.001), SCME (0.31-fold, p < 0.001), SCHE (0.07-fold, p < 0.001), SCEESCME (2.86-fold, p < 0.001), and SCHESCME (0.33-fold, p < 0.001).

Mann–Whitney U nonparametric test was also applied on parameters of drinking water from non-longevity areas in South China versus non-longevity counties in North China, and the results showed significant difference (p < 0.05) in pH (0.92-fold, median value of non-longevity areas in South China was 0.92-fold that of non-longevity areas in North China, p < 0.001), EC (0.06-fold, p < 0.001), Eh (1.12-fold, p = 0.007), HCO3 (0.06-fold, p < 0.001), Ca (0.05-fold, p < 0.001), Mg (0.06-fold, p < 0.001), Na (0.06-fold, p < 0.001), Cl (0.05-fold, p = 0.021), SO2−4 (0.05-fold, p < 0.001), As (0.04-fold, p < 0.001), B (0-fold, p < 0.001), Ba (0.44-fold, p < 0.001), Be (0-fold, p = 0.02), Cd (0.39-fold, p = 0.007), Co (0.36-fold, p = 0.001), Cr (0.34-fold, p = 0.002), Cu (0-fold, p < 0.001), Li (0.09-fold, p < 0.001), Ni (0-fold, p = 0.006), P (0-fold, p < 0.001), Pb (5.15-fold, p < 0.001), Tl (0-fold, p < 0.001), V (0-fold, p < 0.001), Cs (6.83-fold, p < 0.001), In (0-fold, p = 0.006), Rb (8.6-fold, p < 0.001), U (0.04-fold, p < 0.001), Sr (0.01-fold, p < 0.001), Mo (0.01-fold, p < 0.001), Fe (0.52-fold, p = 0.009), SCME (0.17-fold, p < 0.001), SCEE (0.47-fold, p < 0.001), SCHE (0.06-fold, p < 0.001), SCEESCME (2.5-fold, p < 0.001), and SCHESCME (0.37-fold, p < 0.001).

Hydro-geochemical differences

Most of the water samples were fresh water (TDS <1,000 mg/L) (Figure 2) and the others were brackish water (1,000 < TDS <2,000 mg/L). Fresh water accounted for 97.5%, 100%, and 85.71% of samples from longevity areas in South China, non-longevity areas in South China, and non-longevity areas in North China, respectively.
Figure 2

Drinking water quality in longevity areas and non-longevity areas in South China and non-longevity areas in North China. TDS: total dissolved solids; TH: total hardness.

Figure 2

Drinking water quality in longevity areas and non-longevity areas in South China and non-longevity areas in North China. TDS: total dissolved solids; TH: total hardness.

Drinking water samples from both longevity areas in South China and non-longevity areas were mainly hard water. The percentage of very soft water (TH <75 mg/L), soft water (75 < TH <150 mg/L), hard water (150 < TH <450 mg/L), and very hard water (TH >450 mg/L) in longevity areas in South China were 22.5%, 22.5%, 47.5%, 7.5%, and that of non-longevity areas in South China and non-longevity areas in North China were 78.4%, 6.8%, 13.5%, 1.4%, and 14.3%, 28.6%, 28.6%, 28.6%, respectively.

Hydrochemistry type of drinking water samples from longevity areas in South China were Ca·HCO3 and Ca·Mg-HCO3 (Figure 3), and in non-longevity areas in South China were Ca·Mg-HCO3 and Na·K-HCO3. The major hydrochemistry type of non-longevity areas in North China was Ca·Mg-HCO3.
Figure 3

Piper diagram showing major ion composition of drinking water in longevity areas and non-longevity areas in South China and non-longevity areas in North China.

Figure 3

Piper diagram showing major ion composition of drinking water in longevity areas and non-longevity areas in South China and non-longevity areas in North China.

Relationship between longevity areas and chemical composition of drinking water

The elemental content in drinking water is one of the most important factors for human health and may affect the desirable balance of essential elements in the human body (Keller 1978). Generally, by comparison with non-longevity areas in China, the drinking water in longevity areas of South China has high value SCEESCME and low value SCHESCME. Compared with non-longevity areas in South China, TH and strontium (Sr) in drinking water in longevity areas in South China were significantly higher. Hard water and very hard water were present in 55% of drinking water in longevity areas in South China, and in 14.9% of drinking water in non-longevity areas in South China (Figure 4). It has been shown that increasing hardness decreases the toxicity of some metals in natural waters to many biological organisms by providing competition for the metal ions for binding sites in organisms (Ritter et al. 2002). A negative relationship between the hardness of drinking water and cardiovascular diseases (CVD) has been found in many published studies (e.g., Monarca et al. 2006; Zhang et al. 2012). The median concentration of Sr in drinking water in longevity areas in South China was 82.1 μg/L, which was 11.02-fold higher than that of non-longevity areas in South China (7.45 μ/L). In natural water, if the concentration of Sr reaches 200 μg/L, it would be called mineral water. Strontium is beneficial to the human body in terms of promoting Ca uptake into bone and preventing osteoporosis (Zhang et al. 2011; Alegre et al. 2012). The elderly are a high-risk group who suffer from CVD and osteoporosis (Hannan et al. 2000; Tekin et al. 2011). In the longevity areas of South China, the concentration of TH and Sr in drinking water was 157.82 mg/L and 82.1 μg/L, respectively, which may be the optimum level for human health. Elevated levels of TH and Sr were found in non-longevity areas in North China, but the SCHE and SCHESCME in the non-longevity areas of North China were much higher than that of the longevity areas in South China, and SCEESCME was much lower than that of longevity areas in South China, which may have a potential impact on human health.
Figure 4

Sr versus TH of drinking water samples in longevity areas and non-longevity areas in South China and non-longevity areas in North China.

Figure 4

Sr versus TH of drinking water samples in longevity areas and non-longevity areas in South China and non-longevity areas in North China.

The concentrations of As were decreased gradually in Huaiji, Guangning, Sihui, and Sanshui in the order of north-west to south-east, which were in agreement with OC, CI%, and UC, while Cl was the opposite (Table S2, available with the online version of this paper). The concentrations of As and Cl in drinking water in Sanshui were 0.3-fold and 12.35-fold that of Huaiji, respectively.

CONCLUSION

The drinking water of both longevity areas in South China and non-longevity areas in North China was mainly hard fresh water, while that in non-longevity areas in South China was mainly soft fresh water. Most median concentrations of elements in non-longevity areas in South China were lower than those of longevity areas in South China and non-longevity areas in North China. Generally, by comparison with non-longevity areas in China, the drinking water in longevity areas of South China has high value SCEESCME and low value SCHESCME. Compared with non-longevity areas in South China, the concentrations of Sr and TH in drinking water in longevity areas of South China were significantly higher, while the same trend was found in non-longevity areas in North China. In the longevity areas of South China, the concentration of TH and Sr was observed at 157.82 mg/L and 82.1 μg/L, respectively, and considered as the optimum level for human health. The elemental concentrations of As were decreased gradually in Huaiji, Guangning, Sihui, and Sanshui in the order of north-west to south-east in agreement with OC, CI% and UC, while Cl- was the opposite.

ACKNOWLEDGEMENTS

Support for this research was provided by the National Natural Sciences Foundation of China (Grant no. 41472322, 41172310) and the National Basic Research Program of China (973 Program) (Grant no. 2014CB238906). The authors declare that they have no conflict of interest.

REFERENCES

REFERENCES
Alegre
D. N.
Ribeiro
C.
Sousa
C.
Correia
J.
Silva
L.
de Almeida
L.
2012
Possible benefits of strontium ranelate in complicated long bone fractures
.
Rheumatology International
32
(
2
),
439
443
.
Hannan
M. T.
Felson
D. T.
Dawson-Hughes
B.
Tucker
K. L.
Cupples
L. A.
Wilson
P. W. F.
Kiel
D. P.
2000
Risk factors for longitudinal bone loss in elderly men and women: the Framingham osteoporosis study
.
Journal of Bone and Mineral Research
15
(
4
),
710
720
.
Keller
W. D.
1978
Drinking water: a geochemical factor in human health
.
Geological Society of America Bulletin
89
(
3
),
334
336
.
Liu
Y.-L.
Luo
K.-L.
Lin
X.-X.
Gao
X.
Ni
R.-X.
Wang
S.-B.
Tian
X.-L.
2014
Regional distribution of longevity population and chemical characteristics of natural water in Xinjiang, China
.
Science of the Total Environment
473–474
,
54
62
.
Magnolfi
S. U.
Petruzzi
E.
Pinzani
P.
Malentacchi
E.
Pazzagli
M.
Antonini
F. M.
2007
Longevity index (LI%) and centenarity index (CI%): new indicators to evaluate the characteristics of aging process in the Italian population
.
Archives of Gerontology and Geriatrics
44
(
3
),
271
276
.
MEPPRC
2002
Methods for Chemical Analysis of Water and Waste Water
,
4th edn
.
Ministry of Environmental Protection of the People's Republic of China (MEPPRC)
,
Beijing
,
China
.
MHPRC
2006
Standards for Drinking Water Quality (GB 5749-2006)
.
Ministry of Health of the People's Republic of China (MHPRC), Beijing
.
Monarca
S.
Donato
F.
Zerbini
I.
Calderon
R. L.
Craun
G. F.
2006
Review of epidemiological studies on drinking water hardness and cardiovascular diseases
.
European Journal of Cardiovascular Prevention & Rehabilitation
13
(
4
),
495
506
.
National Bureau of Statistics of China (NBS)
2010
Data of the 2010 Population Census of the People's Republic of China
.
China Statistics Press
,
Beijing
,
China
.
Nkono
N. A.
Asubiojo
O. I.
1997
Trace elements in bottled and soft drinks in Nigeria – a preliminary study
.
Science of the Total Environment
208
(
3
),
161
163
.
Ritter
L.
Solomon
K.
Sibley
P.
Hall
K.
Keen
P.
Mattu
G.
Linton
B.
2002
Sources, pathways, and relative risks of contaminants in surface water and groundwater: a perspective prepared for the Walkerton inquiry
.
Journal of Toxicology and Environmental Health, Part A
65
(
1
),
1
142
.
Smith
A. H.
Lopipero
P. A.
Bates
M. N.
Steinmaus
C. M.
2002
Public health – arsenic epidemiology and drinking water standards
.
Science
296
(
5576
),
2145
2146
.
Stefanadis
C. I.
2010
Seeking the secrets of longevity
.
Hellenic Journal of Cardiology
51
(
5
),
479
480
.
WHO
1996
Trace Elements in Human Nutrition and Health
.
World Health Organization
,
Geneva
,
Switzerland
, p.
361
.
WHO
2011
Guidelines for Drinking-Water Quality
,
4th edn
.
World Health Organization (WHO)
,
Geneva
,
Switzerland
.
Willcox
D. C.
Willcox
B. J.
Poon
L. W.
2010
Centenarian studies: important contributors to our understanding of the aging process and longevity
.
Current Gerontology and Geriatrics Research
1
6
.
Xin-min
F.
2006
The research of distribution of longevity population in China
.
Population Journal
03
,
19
23
.
Zhang
B.
Hong
M.
Zhang
B.
Zhang
X. L.
Zhao
Y. S.
2007
Fluorine distribution in aquatic environment and its health effect in the Western Region of the Songnen Plain, Northeast China
.
Environmental Monitoring and Assessment
133
(
1–3
),
379
386
.
Zhang
W. B.
Shen
Y. H.
Pan
H. B.
Lin
K. L.
Liu
X. G.
Darvell
B. W.
Lu
W. W.
Chang
J. A.
Deng
L. F.
Wang
D. P.
Huang
W. H.
2011
Effects of strontium in modified biomaterials
.
Acta Biomaterialia
7
(
2
),
800
808
.

Supplementary data