Depending on whether the global level of fertility is assumed to converge to the current European TFR (~1.5) or that of Southeast Asia or Central America (~2.5), global population will either decline to 2.3-2.9 billion by 2200 or increase to 33-37 billion, if mortality continues to decline. Furthermore, sizeable human populations exist when the 'voluntary chosen' ideal family size is heavily concentrated around one child per woman with TFRs as low as 0.6-0.8. However, the UN population projections to 2300 use a much narrower band of possible future TFRs. If the two-child norm is not necessarily the end-point transition, what would be the consequences of the currently reported low fertility rates being sustained and becoming widespread? We present new projections for 13 IPCC world regions with scenarios calculated on the basis of regular cohort-component projections by age and sex in single-year time steps up to 2300, each based upon a much broader set of fertility assumptions than currently employed. We create three mortality scenarios based upon maximum life expectancies of 90, 100, 110, as well as a series of "Special" scenarios. Even under conditions of further substantial increases in life expectancy, world population size would decline significantly if the world in the longer run followed the examples of Europe and East Asia. In contrast to Malthusian disaster scenarios, our exercise illustrates the distinct possibility of significant population shrinking associated with increasing life expectancy and human well-being.

Contemporary China is facing the threat of rapidly aging population. Increasing portion of the economically inactive part of the population is already putting a significant strain on the Chinese pension system. Health care and social security system are still underdeveloped and also unprepared for this trend. As an attempt to reduce this issue by revitalizing the low birth rate, Chinese one-child policy underwent a significant relaxation in 2007. The expected acceleration of the birth rate however did not occur. Using the panel data from 31 regions of China between the period 2001 and 2013, I have analyzed this issue. My thesis provides the evidence, that one-child policy is not the exclusive culprit behind the continued trend of below-replacement fertility levels. Socioeconomic environment in China underwent a rapid transformation during the past 37 years. One of the socioeconomic factors newly affecting the Chinese birth rate level is the wealth. This is manifested by the inverse relationship between the wealth and fertility and it is known as the demographic-economic paradox. This thesis proves the presence of this phenomenon across the regions of China. It also demonstrates that it could have at least partly counterweighted the effect, which one-child policy easing had on birth rate in 2007. Since the one-child policy has lost significant part of its normative power to other factors affecting the birth rate, I am arguing it is the sign, that one-child policy is slowly becoming redundant on its own.

Organochlorine pesticides (OCPs) were extensively applied in agriculture, industry and public health programs for decades. Based on the persistence and the lipophilicity of OCPs, these chemicals are ubiquitous in the environment and can be accumulated in fatty tissues of animals through the food chain. Even being restricted for years, OCPs are still detected in human bodies. In this thesis, analytical methods for the determination of OCPs were developed and applied for the analysis of cord serum samples. The evaluation of prenatal exposure to OCPs and its effects on birth outcomes as well as the postnatal growth were investigated. Due to the toxicology and carcinogenesis, biomonitoring of the OCP exposure to human is needed. Therefore, an analytical method with high sensitivity and specificity is required to detect OCPs at trace levels in serum. We compared two data acquisition modes of mass spectrometry (MS), namely selected ion monitoring (SIM) and multiple reaction monitoring (MRM). Higher sensitivity and selectivity were achieved by MRM because the background noise was reduced by lowering the matrix effects. Different ionization techniques, including electron ionization (EI), chemical ionization (CI) and atmospheric pressure chemical ionization (APCI) were evaluated. The EI source is a universal ionization technique available with the MS library for the compound identification. The negative chemical ionization (NCI) is more suitable to analyze compounds with high electronegativity. The novel ionization technique APCI was coupled to gas chromatography-tandem mass spectrometry (GC-MS/MS). The APCI source was evaluated by terms of ionization and fragmentation performance. APCI was a soft ionization technique generating molecular ions with high intensity. The selectivity and sensitivity of APCI were comparable or better than the EI source. As one of the largest consumers and producers of OCPs, China has suffered severe OCP pollution. Previous monitoring studies reported detectable levels of OCPs in human bodies. However, studies concerning the prenatal exposure to OCPs in China are limited. Due to the vulnerability of fetuses, the effects of prenatal exposure to OCPs could be more severe than those of adults. We collected cord serum samples during the delivery period in Wuhan, China and measured the OCP concentrations to assess the prenatal exposure by using GC-MS/MS. Compared with other areas in China, the OCP levels in Wuhan were comparable in this population. The identified predominant OCPs were β-HCH and p,p'- DDE, with geometric means of 8.67 and 33.9 ng/g lipid, respectively. Slight positive associations were found between α-HCH and β-HCH, and between o,p′- DDT and p,p′-DDT, which indicated similar exposure source of these chemicals. The obtained results showed that HCH levels were associated with maternal age, body mass index (BMI) before pregnancy, education levels, and passive smoking. Associations between the prenatal exposure of OCPs and birth outcomes were investigated. The sex-specific relationships between the OCP exposure and birth size were indicated. Concentrations of β-HCH were inversely associated with birth weight and ponderal index for boys, while for girls these associations were not significant. Our results suggested that the prenatal exposure to OCPs exerted negative effects on the fetal growth, and precautions should be taken even though the OCP levels were relatively low.